Why shouldn't be? What role would want it have?
OKW having a doctrinal counter to m3/UC/WC51 and to snipers makes perfect sense.
But it doesn't make sense to have early game doctrinal unit that has no counter when it arrives, while it counters literally all units on field at the time.
See the problem yet?
High cost and low armor keep 221 in check.
Yet again(as you seem to completely ignore it every single time), no allied faction has counter for any decently armored light with turret in very early game 221 arrives.
You want stronger or cheaper aka more spammable 221? Sure, have it, but you have to make sure allies actually have a counter for it. Allow rifles to start with AT nades, make something so brits can use AT at T0 without fuel investment(you know, like puppchen and ost fausts) and lower cost of soviet AT nades from 25 to 10 and we may start talking about buffing or making 221 cheaper.
221 itself may not be most cost effective thing, but as already said, much like oversoldaten, its not suposed to, because its balanced around being upgraded.
If that wasn't enough, you seem to firmly believe once its 223, it should be planted on resource point and forgoten, like a cache. It shouldn't, it should then be used more aggressively, because now it can survive more and do more and shared vet allows it to vet up fast.
You want to make a dough and you complain that flour alone doesn't cut it. Well, flour alone isn't supposed to work, you're supposed to add water(upgrade) and then it'll work.