T1 was originally designed to be played with an elite infantry, specifically guards. However, this prevents any commander without elite infantry from being part of the meta and it makes it hard to balance the game around. By adding a lite AT option you open the door to more commanders while preventing Soviets from getting rewarded for going T1 if they make a mistake.
Right now penals have some insane bonuses and they still aren't used every game, which means when they receive their nerfs they will be even more unattractive. The tier has to provide at least a modicum of AT since otherwise penals need to function as an elite infantry unit (you only get 1 or at most 2), but not dominate the early game.
If you think PTRS penals are outrageous you need to provide a functional way to balance the meta.
In fact all tiers currently have access to some form of light AT except Soviets. Wehr: AC, pak, PGs in T2 and grens in T1, USF: M20 w/ zooks, AA HT as light AT, Brits: 6-pdr. So the only unusual one is Soviet because if you go T1 then you end up in a place where if you don't win big early you lose. This means penals have to be extremely powerful, and it is boring to watch as it steam roles everything early. Instead provide more depth by allowing the game to continue on with more balanced play.
No, that is just the COH2 way. People forget you can tech T2 and get a ZiS if you need to, they're just used to clicking the lazy buttons of Elite Inf docs.
Wehr T1 has no AT.
USF has no AT unless you TECH zookas which is a fuel/tech and muni cost. So technically not just T1.
UKF has to tech to 6 pounder AT guns.
OKW does have the raketen and Sturm pios but yet they struggle with AT more than any other faction in the game since both are kinda shit.
Soviets can get T2 right at the start and build a ZiS for no fuel at minute 1 if they want. Then have access to what is considered one of the most useful MG's in the game as well as Cons with AT nades should they want them. Also the best healing in the game for the least cost. T1 has 2 man snipers which are super powerful on their own, along with the M3 which is also useful. Now, with all of this already quite strong early game options does anyone think that Penals need PTRS or that Soviets need AT in T1? You're out of your minds.