My favorite para tactic is to have 2 paras w/ lmg do the main assault and one Thompson paras come in on a flank and hopefully the wipe. I think the Thompsons are fine but that lmg are too effective. The grenadiers with a single one are fine. Obersoldaten are crazy. Double lmg rifles are crazy too. Paras with lmg and vet 2-3 are nuts as well. I don't know a solution without ruining lmg entirely.
At least allied LMGs are locked behind doctrines.
Against axis you'll inevitable get to the point where LMGs drop your models before you'll get in effective range, its specifically bad for soviets as conscripts are pretty much AT nades on legs that can cap in late game, USF can at least respond with paras or M1919 but still need to pay a hefty muni cost for that, premium cost compared to what ost or OKW pay.
excellent =/= not total garbage.
Assault Guards would see more use if they were in a better doctrine, but as of now they are lack luster which doesn't help lend lease at all.
No, they wouldn't, because they have no utility, no scalability, no survivability and no role that wouldn't be filled already by better performing troop or by more universal one for much lesser cost. Unless they suddenly became 0CP call-in, there is no reason to ever get them and the only reason you get them with lend lease doctrine is because you want M5 and went T4.
They are garbage no matter how you want to spin it. They have even less value then irregulars.