I do not see the point in the 7th person. This upgrade comes so late so the Guard or Shock Troops will be your main infantry anyway so as not to lose. As a combat effectiveness, upgrade weapons such as PPSh or SVT are much more effective and finally starting to be a real combat unit (moreover, upgrade weapons come to 1-2 CP). So to throw an AT grenade, what their main role still remains, they can perfectly well without the 7th person.
. 7 man increases durability, decreases reinforcement and slightly increases firepower in cover. A very big draw imo is 7 men can fully recrew a team weapon without losing the squad, somehting that could be game changing late game. What's more, RNG is RNG and 7 men trying to throw a snare are better off than 6 when things like KTs and Brummbärs prowl.
It comes late that is true but the dev team were worried about increasing the existing t3 powerspike. To come sooner the T70 would need toned down, which I'm fine with but many people here are unable to fathom multiple changes at a time