You say no AT nades means no protection against light vehicles. Ostheer has no light vehicles until t2.
By this time there will be a considerable resource imbalance, mines everywhere and AT guns behind the MGs.
The light vehicle "hard counter" is hard countered by the same tier as the Maxim. T2 hard counters its own hard counter.
You can't argue that you're giving up AT abilities when you clearly get excellent AT abilities with th same tier.
So the MG spammer is rewarded with both map control and fast access to the hard counter to his spam.
Please explain if you think AT guns are inferior to AT nades in taking out light vehicles.
And Maxims are just as vulnerable to indirect fire as any other unit. They can move quickly and are just relocated when the mortar rounds start going. The long mortar cooldown and mobility of the Maxim (along with the squad size) mean that it is NOT very vulnerable to indirect fire.
(Most of all I just hate boring, static games. I lose to conspam too but I can enjoy those games because I'm not constantly running off the map.)
ZiS guns do not kill 221s/222s/251 in a single shot - it's actually really easy to avoid them and just run around the map killing everything else. AT grenades (or guard M3) are a lot more reliable because the engine damage means that they're probably not going to get away. (Especially if you combine an AT grenade with a ZiS, or a guard M3 which a more standard build can easily do)
Moreover the 222 does WAY more damage up close than at range - AT grenades force it to stay at range. You can just drive straight into a Maxim, vehicle block the retreat and wipe it extremely easily.
Basically without AT grenades the 222 gets to run around the map unchecked, while also bleeding you harder than if you had Conscripts around with AT nades - and god forbid it flanks your ZiS gun while you have nothing but 6x Maxims on the field - you just gave your opponent a free AT gun.
Additionally, without AT grenades your ZiS gun is going to be worthless against tanks. They'll be able to just drive straight at the gun and circle strafe it without fear.
Maxims are more vulnerable to mortar fire because of the way in which mortar mechanics work in this game. Basically what happens is the mortar shoots, at this point in time it places a marker on the squad that it is shooting at(or barrage circle). The shot then "scatters" away from that marker based on the distance traveled, vet, bulletins, etc. A deployed Maxim is stationary, meaning it will get hit a lot more often than say a Conscript squad that is walking around - and could easily walk outside the scatter AoE without even realizing that it is getting shot at, simply because Cons are almost always going to be on the move. You don't even have to use the barrage on the Maxim, you can just keep right clicking with your mortar selected, or attack ground where the maxim is meaning the maxim squad is going to have to relocate constantly. So yeah, long story short, all set-up teams are more vulnerable to indirect fire than normal infantry squads.