Well, I wouldn't say that Riflemen vet bonuses are bad in comparison to Penals. They get better RA (and start with better RA too), can have AT-snare from vet while having option to still be completely AI unit (double bars).
They have more EFH since they start with 6 entities and they also get the vet 1 ability. Compare their vet bonuses with the ones Paratroopers get (they start with same DPS long range) and you will see that they are superior.
My original point stands, "many Soviet units have superior vet bonuses."
Finally riflemen should not be the benchmark, the unit was designed to be OP to carry the faction. Unfortunately other starting infantry have become stronger.
And conscripts vet was buffed/reworked only recently (depends on how long ago you meant saying "older days" though).
PPsh conscript not only get some of the highest RA accuracy bonus and a damage reduction ability they also get of the highest accuracy bonuses x154 in total, a weapon upgrade plus a CD buff.
Basically, cons are purely defensive/support unit,
penals are damage dealers and survive long enough purely because of high total HP,
riflemen are all-rounder with different options for upgrades which can result in high AI efficiency too while having good RA.
Penal get received accuracy at vet 1 via ability and at vet 3. Their DPS bonus are probably the highest among all infantry while they start with the same far DPS as Paratroopers a 380 CP3 unit.
At vet 3 Penal PTRS are superior AI than vanilla riflemen almost at all ranges, Penals vet 3 probably beat BAR vet 3 riflemen.