Luftwaffe supply drains all your manpower if you spam it ans CASconverter drains all your fuel leaving you without that "so needed" tanks, about Lend lease, i know that ammo isnt so popular, but the plane is easy to kill, all of them have something. About KV-2, its a really powerfull whipping machine, the problem is that it needs LoS, it would be great with guards, IMO it's a great unit in the wrong comander, It would be k on NKVD tactics, but thats just a theory
The point is that Luftwaffe does not drain your MP. It's up to you to decide if you want sacrafice 200 MP. From 2v2 perspective I can say that I often have around 600MP so I can get extra ammo without any penalties.
Just yesterday I had really intensive 2v2 and I was able to spend over 1000MP in exchange for ammo. But it was up to me when to do it.
CAS is same thing. It's up to when you want to convert.
Same thing for Lend-Lease of OKW conversion.
With KV-2 doctrine, it's different, nothing is up to you which is huge penalty.
As for the rest, you are right KV-2 is not that bad, but when you consider 14CP, costs and only 800HP, well... It does not look very good. Still, ISU is better at wiping and comes with better doctrines.
But still, over 11secs reload and the trajectory of the shell puts it way behind ISU in terms of wiping.
Barrage mode seems to be an answer but with Ostheer off maps, and OKW Jadgtiger and Sturmtiger, it's like shooting your own leg.