His point is still valid since you failed to disprove him.
Anyway it can be countered quite easily, GrW34 and Rak43. It does need a MP cost increase however, around 225 MP would be fine. FP spam is a thing indeed.
You should look up the meaning of the word "valid" as it applies to arguments.
Turning to the OP's point, fighting positions are not even close to OP. Attacking ground with mortars or racketens works fine. Heck, they're so fragile that you can actually charge your racketen directly into the cone and still win (not that you should.) If you can get a line on it outside of its cone, you can even kill it with small arms. All you have to do is move every once in awhile before the grenade goes off.
Since they are the USF's only real non-doctrinal early answer to buildings and one of the few things that can prevent the USF from being rolled by kubels in the early game, they pretty much have to be as strong as they are. Given the ease with which they can be countered, there is no need for a price increase.