The road to making t1 viable lies in fixing t2 and not making t1 better in every way.
Well yes and no.
The root of the problem lies in how the tiers of each faction relate to each other.
To start with EF armies have 5 tiers whereas WF armies have 4. Furthermore WF armies open the game building all their starting units from t0, where as ost will generally build t1 and soviets can choose between t0, t1 or t2. Sovs on the surface seem to have the most variety and flexibility. But in reality its a bit of a mess.
The issue for sov t1 is a lack of early map presence due to penals and snipers being expensive and m3 not able to capture points. The result is sov t1 must be strong to regain the territory it lost.
The solution to me is to re examine all factions and the timing/cost of each tier as well as general starting builds and make educated guesses as to when each faction will move to each tier.
The first thing that becomes apparent when doing this is sov t1 is always slightly behind and if the axis player plays aggressively and the map is small and/or allow for easy cutoff then it becomes difficult to catch up.
Secondly I would make sov t1 similar to ost t1 in cost, so that both factions can essentially field their first 3 units at around the same time, note, I am assuming ost goes mg, gren and sov goes con, penal. If sov t1 still lack field presence, and i am not advocating penal spam, then i would lower the cost of penals and adjust penal stats.
Basically I would make t1 the standard opening building for sov with penals being their core army, supported by cons (merge, sandbags, at nades).
M3 I would nerf as follows, reduced accuracy when moving. Flamers reduced damage when m3 moving so as to reduce the dreaded chasing retreating squads. Vet 1 ability, can reinforce.
Penals I would make optimal at midrange, leaving role for cons and shocks at short range. I would add flamer for 120 muni and add increased damage received when using oorah. Adjust stats so they are similar to usf rifles but don't vet quite so well.
For infantry AT I would add guards to t1 but lock them behind a fuel upgrade. Guards would be optimal at long range and have PTRS upgrade for 120 muni. Grenades would be tied to at nade upgrade. I think this type of structure allows for maximum variety and flexibilty but not so accessible that every option is available.
The goal would be to make each unit have a clear definable role, with upgrades that are priced appropriately so that they have opportunity cost and are not spammed. For example going penal flamer and guards with ptrs will not leave many muni for mines or sweepers. Going guards and at nades will delay t2 or t3 etc etc.
For t2 I would lower mp cost but increase fuel price, that way effectively killing the maxim spam opening but making it affordable if player goes cons spam or t1 opening and wants support weapons from t2.
The main idea is really to try and standardise soviets to some extent and balance from there.