Why? They are both 600mp units. They should be equal in cost efficiency but different. 105 firing faster, ML-20 doing more damage.
Don't know, why PaK40 is better then ZiS-3 for the same cost?
Why grens are better then cons?
Why pwerfer is better then katy(this will get hot

)
Why ost sniper is better then sov sniper?
Why mortar is?
Why ost mht is better then us mht?
The list goes on and on for same role, same cost units of old armies.
The only problem I see with the ML-20 is the Recon + Dive bomb combination. A first start (at least for 1v1) would be to take away either the recon or dive bomb from the Elefant and CAS doctrine respectively.
The problem isn't as much stuka+reckon, but these two being in meta doctrines while ML-20 is pretty hipster stuff.