A lack of naval support wouldnt rlly be a big deal with the IJA having engaged mostly on land battles, and there were tons of land battles on the Pacific, maybe more than naval battles actually.
Land battles that included naval support, a feature that's not very realistic in CoH2 battles. Air strikes however are a different issue, you just make the descriptions vague so it's not clear if it's IJA or IJN based aircraft doing the attacks.
I would put it in the perspective of the following:
About Japanese units not being able to compete against the British or Germans in an open field battle in Coh2 I dont agree at all, this is kinda the point and what Im trying to show in this thread actually. Take a look at the Ho-Ni II TD I included for example or the Type 4 Ho-Ro, these could technically take out a Tiger I or even a KT, so these two could easily be a late game IJA vehicle, and I left out a few other possible late game vehicles.
Also considering that there are already some in game units such as the Soviet Zis gun, bazookas, among other that can take out a KT or a Jagdtiger from the front, adding some other units which actually had better pennetration value such as the Ho-Ni II (120mm pen) or the Type 41 field gun (around 100mm pen), I dont think it would look anymore unrealistic on that aspect, also its not like Coh2 is an example of realism either. Aneways so these two IJA TDs for example could easily be around the same tier of the Jackson or the Su-85 regarding penetration values.
Japanese anti tank weapons would be as realistic as ZiS and bazookas penetrating King Tigers fron the front: both are unrealistic to the point of ridiculous.
Of course the problem with that argument is that it just reinforces the sheer unrealism of the game and how a Japanese faction has to be equally ludicrous in order to be feasible in said unrealistic game. I still don't buy that, because it's a mentality that accepts increasing implausibilities just to accommodate an almost implausible scenario. I rather they just make a CoH3 featuring IJA, hell it'll make more money for them, AND be less of a headache to balance and tweak.
ALso to add, you're not just trying to design units to perform against other units they've never fought agains, but also design a faction that would, presumably, have a distinct style of gameplay. Of course that's not withstanding the idea of IJA Rifleblobs blazing though Churchills by equipping 81mm RRs. Come now, we all know that's the first thing we'll do once we unlock that upgrade at T4!