Read my post again. I didn't say that the bren and PIAT have a higher tendency to drop. I said that they seem to drop more because its possible for them to drop as soon as the IS goes from 4 models to 3.
That's not how that works. The reason why it happens/happened to Guards is that PTRS's have a slot size of 1, something carrying a PTRS cannot take another weapon. Tommy Scoped Lee's have a squad size of 0, if you try and pick something up with a Tommy squad that's been reduce to 2 men with Scope Lee's you can pick it up.
Except, you know, the G43 doesn't come on squads that have other droppable weapons, so it doesn't cause the same problem.
G43's count as slot weapons but have a size of 0, so they don't stop you from picking other things up and if you lose models they will keep the item you picked up. I brought this up to point out why what you said isn't correct.
STG44s take up weapon slots, but they do not work the same way as scoped enfields. You will never see a schreck pgren squad with 2 STGs and no pshrecks, because the Panzerschrecks have priority.
They do not take up weapons slots, you can still pick things up if you have StG44s (Ober StG44's do count tho). The reason why I point out they were slot weapons is just because something is classified as a slot weapon does not mean that it takes up space.