Thinking that the vehicle is just a taxi to get to the battlefield is a very dangerous concept. Infantry and armour are the two key component of the combined arms team, and trying to ignore one has been the undoing of many an army. It was one reason the idea of standard infantry battalions, able to do anything (lifted in APCs, lifted in PMVs, lifted in helos, walk etc) was always aspirational, and not really practical. It’s fine in theory, but in the real world where there is only finite training time it doesn’t work. You either have to specialise in something and be good at it, or specialise in nothing and be average at everything.
It was no surprise that the same rifle companies kept getting allocated to the ACRs every exercise, as by the time you got them proficient at mechanised ops, why would you start again with someone else? Having been an APC troop leader in 3 Bde in the pre-Beersheba days, after having previously been in 1 Bde, it was pretty clear to me that the army would never achieve a high standard of mechanised ops with standard infantry battalions. There just wouldn’t be enough experience outside of the ACR. Considering a Beersheeba brigade is a mechanised brigade in all but name, that was never going to be the best way to do business, IF a proficiency in mechanised ops was desired.
The biggest advantage of going back to dedicated mechanised battalions is you can actually design an orbat that makes sense for mechanised ops. For example, a standard infantry battalion that is designed to be light, and only lifted by APCs occasionally, can’t have vehicle based mortars. A dedicated mech battalion can, and probably 120mm mortars to boot. The impacts to Land 400 Phase 3 are obvious. Same with DFSW platoon. With standard infantry battalions, the DFSW platoon was going to be lifted in Land 400 IFVs (with 30mm cannon and 4000m+ ranged ATGMs) to delivery them to the battlefield to employ their .50 cal, GMGs, GSMGs, 84s and 2500m ranged ATGMs. What would be the point in that? A proper mech battalion can have have dedicated DFSW vehicles, just with a few dismounted Javelin/Spike in the back in case they have to do a dismounted anti armour ambush or something.
As you’ve stated, the disadvantage of dedicated battalions is a loss in flexibility. This is true, but it is true of a lot of other things too. For example the JSF for the RAAF isn’t going to be much use for anything more than high end warfighting, yet no one is arguing for something more flexible at the lower ends of the warfighting scale instead. If the nation desires a high end mechanised capability, and the fact we are spending tens of billions of dollars on CRVs, IFVs, tanks, under armour breaching etc suggests we do, then that loss of flexibility can be accepted. Besides, it really isn’t that hard to dismount a battalion for some peacekeeping somewhere in the world - we’ve done it before. We’ve even re-roled gunners and engineers into light infantry without issues.
The only problem with dedicated mech battalions is the training burden on the infantry. The new IFVs are going to be incredibly complex to operate - just as complex as the tank. The previous approach the infantry used for M113 training isn’t going to cut it. Unless we integrate RAAC personnel into the mech battalions (which is on the table), probably the only way to achieve a high standard of training is to create a specific career stream for mechanised infantry. Soldiers would join up either as ‘light’ or ‘mech’, and serve their careers in one or the other. That is clearly a significant cultural shift for the infantry, so it will be interesting to see what happens.