Oh they are definitely with a different focus MC-55 to EA18..
But the MC-55 has much longer reach, and broader focus as an intelligence asset.
EA18 just doesn't have the range to do long intelligence gathering missions. It is a short ranged fighter platform fitted with Electronic warfare.
You talk as though the Super Hornet and Growler are interchangeable (SH can do EW missions, 36 Fighters etc). They most definitely are not, with significantly different installed components, loadouts and discrete training requirements for the differing mission sets these platforms undertake.
They are both short ranged fighter platforms. They are not interchangable, obviously. However, their physics limitations and capabilities are broadly similar in comparison to a G550 based or 737 or C130 based aircraft or even a F-35.
My point is E7 and MC-55 help and assist the load off the EA-18. Obviously the USN doesn't have either of those aircraft, so it has to use EA-18 for everything.
You talk as though the Super Hornet and Growler are interchangeable (SH can do EW missions, 36 Fighters etc). They most definitely are not, with significantly different installed components, loadouts and discrete training requirements for the differing mission sets these platforms undertake.
What matters is the total capability, not the individual unit. They are based off the same fighter platform, the F-18 superhornet. So my comments about a sorted platform and it being twin engine, and EW is true. I don't know why that would upset people, both the EA-18 and the F-18F is a twin engine platform, and sorted in terms of capabilities. The F-35 can't fire LRASM, which is true, and it is single engine. Is this a shocking reveal? I hope the PLAAF doesn't get hold of this secret information.
Replacing the entire Superhornet platform capability (which includes Growlers and Fighters) would need to replace total capability, not just an individual capability of just the F-18F or the EA-18 Growler. Unless you think the RAAF is going to keep all the logistical support for the EA-18 just for 12 airframes? Unique engines, unique airframe, unique upgrades, unique maintenance and technical facilities. They are tied together.
I am also confused by the way you are talking about SH and Growler doing missions separately. AFAIK that is not how they are intended to operate in the battle space. You are not just flying 2 growlers into theatre by themselves, nor do you just fly 2 F-18F as some sort of wonderweapon. Neither is going to go it alone. Wouldn't it then make sense to talk about the capability of a combined platform rather than "mOrE SuPaHoRnEt for the win!". I don't see the acquisition of more of one type, adjusting the ratio, for the Superhornet platform.
But these are my opinions. Others may vary.
EA18 was a fast and great way to get EW capability at the time, we were acquiring the same platform for other reasons. Now however, much of those capabilities could be transferred to more effective platforms (MC-55 and E7) which are bigger, longer ranged, have more growth potential, cheaper flight hours, better able to handle the workload and F-35 IV block IV and future blocks making the embedded F-35 EW capability much greater on F-35. Its not here today, but in 5 years it will be.
So in the future, no, not sure more Superhornets are the future, as their mission is going to generally be acquired by F-35 and MC-55, E7 platforms, which will do it better. They will still be somewhat relevant, and the USN has less opportunity due to it needing a platform that can take off from carriers. But I am not sure more acquisitions are required.