It is a MPF v MBT because the latter can do the former, but not the other way around.
How much is a base Ajax going for? How much is this turret going for? How much are the integration costs? As you point out above, the ammo goes into the hull too - so that's a hull redesign. How much? And without being cruel; how many delays will occur on this program noting that the Brit's haven't had an AFV program go right in decades?
Firepower? It has a 105mm gun. The 105mm that CR2 forced the Leopard and M1 to replace. At a time when 120mm is unlikely to be feasible and nations are looking at 130mm or 140mm. The firepower isn't close to being equal.
I'd be surprised if it could exceed a MBT in mobility. A CR2 possibly; an M1 or Leo 2 very unlikely. Even a really rough check shows that the power:weight of an M1 is about 14% higher. Comparing to our AS4's (which have a higher power to weight ratio than the M1), it isn't until you get into pretty close country where the AS4 starts getting more maneuverable. I don't see how the Ajax can do that - noting that the MPF will weigh more and have even lower power:weight.
Armour wise, it's not just MBTs that a CR2 or the like can shrug off - it's all the other bits. The proliferation of 30mm+ guns on the battlefield won't impact a MBT (much). But they'll pose a significant risk to an MPF. I know that the add-on armour to Stryker MPF claims to stop a 30mm from the front and that Ajax is probably designed against 40mm; but is that with or without add on armour? Noting that weight increases because of add-on drive down your mobility. It'll still carry significant weakness on its side (the armour on packages for other MPFs increase to a max of 14.5mm and close 155mm splinters) that will be able to be penetrated by anything. And remember, the ATGMs and RPGs being thrown at these things are generally designed to stop MBTs; and there are literally tens of thousands of tanks still on battlefields around the world. A 100mm T-55 gun is still going to K-Kill an MPF.
I'm not saying Ajax is a bad vehicle; ignoring procurement it'll be a fine vehicle in its niche. Just like every design. And an MBT cannot do what a Ajax can do (actually - MBTs are smaller than our CRVs...). But for what a tank offers in support of the infantry during a close in-fight (especially in close or urban terrain), the MPF cannot replace the tank. Tanks aren't about killing other tanks only - that's a fallout of planning for operations in West Germany. They do that well, but they have always been (and the Australian Army has always used them) as the other half of the symbotic close assault team. They offer intimate support to the infantry at the most dangerous part of the battle - and they need the thick armour, the big gun and the good power in order to drag up comms, protection, firepower and - most critically - shock action.
You're again arguing for a capability, but the trend clearly shows the UK will ditch armored forces for the forseeable future.
With roughly 120 tanks, the UK can only arm about 1 brigade plus a training unit. But as we've seen a recent halving of the fleet, we might see a complete withdrawal of tanks from service.
It is a common military tradition of effective armed forces, to prepare for the worst possible situation. The British armed forces have 4 serious enemies to prepare for: Russia, hybrid forces worldwide, MoD, and British government.
The Army must create a contingency plan for a decision to cut tanks entirely, and that must include some organic firepower beyond the 40mm offered by the Ajax.
I'll answer your questions in a chronological order because multi-quoting is a tedious task on mobile:
1)The Ajax is in production for the UK Armed Forces, and is supported by multiple facilities outside the UK, and by a major corporation that seeks to keep producing and improving the vehicle in the long term.
The Challenger is no longer supported by industry.
During my service I've worked with a ridiculous amount of ultra expensive equipment with an almost as ridiculous amount of suppliers.
My section of 30 men and women had a total of maybe 9 rooms in our floor, and every room contained RF equipment worth several million dollars.
FPGAs, amplifiers, cables, etc that we threw out on a regular basis, always went for several thousand dollars to tens of thousands of dollars.
I'm right now in the process of discarding roughly $1 million worth of equipment, primarily spectrum analyzers, that only need a minor fix. Replace a screen here, a few capacitors in that one, a filter block in the other, basically fixes that would cost us no more than the usual tip for pizza delivery.
But the company that supports us labeled them as obsolete and can no longer source spare parts for us, so we have to discard them.
How long does it take to acquire a brand new replacement? Roughly 2-4 years.
Now, apply the same issue to a tank, that has infinitely more components and complexity than the equipment I described.
Having a supplier with facilities and spare parts only a few hours drive, is absolutely vital for efficient operation.
Lacking industry support for even a portion of the system you're operating, is a death sentence.
Unless the MoD chooses to upgrade the ENTIRE tank, it's doomed. And I just don't see that happening with the current way forward.
So don't ask how much is an Ajax going for. Ask whether the Challenger 2 is going anywhere, and how much it would cost to bring another 50 year old platform into service today that has 0 commonality with other AFVs.
The Ajax is already in the armed forces, it's produced today, supported, and its development is funded by other entities to save the UK money.
2)The turret is the truly expensive part here. But the Challenger 2 must get both a brand new turret and a vastly redesigned hull. The Ajax on the other hand, only really needs a new turret, so it's a much smaller expense. Not to mention there are mature platform-agnostic turrets on the market already, whose development was more or less finalized and only needs the British touch. RBSL's turret for the Challenger is still in very early stages because it wasn't chosen yet.
3)Integration costs are only really relevant for the turret's systems.
4)The hull ammo stowage requires a redesign of the Challenger 2's hull. Not the Ajax.
Putting ammo in an empty hull of a former APC is easy because the space from the troop compartment already exists there.
The Challenger 2 needs a hull redesign because its ammo stowage is too chaotic and made for 2 piece ammo.
5)Delays will be minimal compared with buying a new tank from elsewhere, because much of the logistics and facilities for this specific AFV already exist, in the UK.
6)Turrets for these light/medium tanks are pretty agnostic when it comes to guns.
You can use 105mm when you think it's enough. But there is no inherent problem in using a 120mm or even 130mm gun.
A 120mm armed CV90 was demonstrated many years ago. A 130mm is possible, especially considering that such vehicles tend to have a much higher potential for ammo stowage anyway, which is perhaps the 130mm 's biggest disadvantage in MBT applications.
The MPF offered by GDLS for the US Army was cheap to develop, and is pitched as the low cost contender, because the expensive part of the hull already exists - the chassis. Remaking the superstructure is dirt cheap.
7)Power to weight is not really a super important factor, but I agree the CR2's power/weight ratio is abysmal.
When the UK wants strategic mobility above all, it starts making sense to rely less and less on MBTs. They're cumbersome beasts.
I'm criticizing the policy of 100% very long range deployments and 0% deployments in Europe, but if they already go that way then it makes sense to go light. Hence the move towards the Ajax as the core AFV anyway.
MBT development is striving for as much weight reduction as possible anyway.
8)30mm guns, IEDs, RPGs, etc, are no more an issue to an MPF than to a tank.
Before I continue with my argument, here's a rule of thumb: For a given weight, a tracked platform has a higher potential for armor protection than a wheeled one.
I've seen the Eitan a few years ago when it was just shown in the media for the first time. I have a few friends in the agency that develops it and I've visited the base in which it's tested a few times.
Obviously, Israel is still not a NATO member, yet, so we don't have the STANAG system. We have something of our own. But at a GVW of 35 tons (maximum weight rating the chassis can handle) when it clearly has a few tons to spare for growth plus a several ton turret, it achieves a level of protection that is higher than STANAG 4569 level 6 for not only the front, but the sides as well. The side armor modules contain 2 passive armor plates, each roughly level 4-5 @90°, plus a SLERA array sandwiched in between them, which can only officially go as high as level 6 because it's the maximum level (most if not all modern western ERA are labeled level 6 because of this, for marketing).
It also affords the Eitan protection versus single charge warheads at 90°, and some protection versus tandem warheads from the front (front engine also contributes to dissipation due to volume).
Take that weight plus the rule of thumb and apply to a tracked vehicle. Make it 42 tons to account for the larger gun plus ammo, and even more armor.
The ASCOD 42, for example, has significant amounts of side armor, NxRA obviously.
That's the same armor tech used to upgrade the Leopard 2SG and 2PL, Merkava 4, Leclerc, CV90 AFVs and so on.
I have no doubt an AFV weighing 40 tons can protect itself very well from artillery, RPGs, mines, IEDs, and ATGMs.
And with APS that can defeat anything from RPGs to APFSDS, it should be quite survivable for an expeditionary vehicle.
