Firstly, the photo shows Thompson at different dates from 1942 to 1945. Secondly, this is not a historical game. This is a game based on the Second World War: in one order the “conscripts” of 1941 and Katyusha ZiS-6 of 1941 together with the IS-2 of 1944.
And, No thanks, why replace the excellent Shock Troops with the mediocre Assault Guards. If it is valid to make them a unique unit of middle distance, between the Shock Troops and the Guard, and for this they just need the Thompsons (after all, they have good damage over the medium distance), can still absurd the replacement. Now there is no point in replacing.
It tried to be somewhat historical before other 3 factions came in...maybe.
Because the Assault Guards are just there, they're made to have their own icon, weapons stats, their own usage intended in mind, and I suggested them to be upgradable with 3 Thompsons while also being able to have the PPSh-41 so they would be more of like Shocks but also being able to do some sort of a damage (especially on high vets) from their rifles, so it's like an upgrade for the Rangers, and they still would have their 3rd weapon slot and even with the PTRS upgrade, so they would be perfect for just having a more diverse gameplay without being too similar to other units and not too UP-OP.
And there is, for example, a doctrine with a 120mm Mortar, PPSh-41 upgrade for Conscripts, and then...Shocks, which doesn't seem very useful and logical, so placing these Assault Guards would allow you go for the Thompson upgrade if you really want, or for the PTRS upgrade so you don't rely on the ATGs and tanks with sometimes Snares alone.
There are just too many Shocks and Guards, they're nearly in every single doctrine.
Just let the players understand if they need them this way and if they won't-fine, but still, I think it's an idea worth a try, considering the Grenade and the Vet 1 are going to be fixed.