In how many games do you never need either AT or vehciles/tanks?
Close to zero, I think.
Your investment in AT or vehicle is far from deadweight. Maybe the german bunkers force you to tech earlier than planned, but what you build from it will hardly ever be wasted.
And remember that the mg on the bunker costs him ammo too. AMmo he can't use for mg42s.
If the OH player is building bunkers, you can't be dealing with gren spam at the same time. He can't use the same MP twice.
my 3rd paragraph which u kindly omitted explained the reason why its deadweight. it forces an early tech to a battle where anti tank weapons are largely useless and swarming with its very counters, infantry. a common reaction from german players would be pgrens + grenadier push, which would then shit on conscript spam AND AT gun. or another mortar squad to if the soviet player went maxim spam.
a bunker isnt exactly expensive and neither are grenadiers. unless u were taking major casualties from molotovs, 150mp is pretty easy to cough out.
however, what is most problematic is the speed of bunkers being built. just force a retreat on an important cutoff, plan ur supply links beforehand and the time for soviets to reinforce and trot back, it is enough for a bunker to cover that cut off.
now the soviet player will only have conscripts to deal with a bunker, forced to get t2 and AT gun (might be a gg if he went t1), while the german player has already bought enough time for AT guns counters and coincidentally, both counters are also good at killing conscripts. so now the soviets would have been starved off fuel/map control and pretty much lost the game.