No it's not. The ML20 has far too much range, to expect a stuka zu fuss to take it out, against any reasonable opponent.
Also, I'm not seeing any solutions here so far...
There are none. Someone thought that ML-20's weren't being built because they were underpowered. They weren't, it just that everyone has CAS and the ultra-efficient two-click counter to ML-20's. The old ML-20's were okay (don't know about the OST ones). Unless the gun can survive a stuka strike, they won't be built. And now that the ML-20 is batshit OP, I'll load out CAS in every team game. If the strafe's aren't working (which they shouldn't), at least I'll have massive minefields, unlimited rifle grenades, and no ML-20'S.
Giving the ML-20 a slow crawl speed or making the gun survive a dive bomb would have worked.