I think what needs to be considered with penals are their direct equivalent Pgrens. I never see a game without Pgrens, either spammed or just used. It's rare to see a game with Penals. Pgrens combine awesome AI which will drill through all Soviet units with the exception of doctrinal Shocks. Meanwhile they can also upgrade to shreks and be able to destroy most Soviet tanks in a couple of volleys whilst still having reasonable AI and gaining plenty of vet which will increase their AI.
Meanwhile, Penals have okay AI (it's too easy for the enemy to either run forward or rifle nade them or have an MG42 or be pgrens)and zero effective AT (satchel is too easy to dodge). Compare it to Pgrens and I think I know what comes out on top. Both units currently costing the same just takes the biscuit.
I think you hit the nail on the head. To get Penals you have to go T1, which means you have 0 effective AT until you can get t3/t4, which means you really struggle against an early FHT/get picked to pieces by upgunned SC... Once again this forces you to go Guards, which are also more MP, and reduce the amount of Cons you can field, reducing your capping power and potentially leaving snipers (why else would you go t1) unsupported.
And it's just not viable enough to go Sniper/guards/penals. Together they're too MP intensive for what they offer, when Con's can effectively do what Penals do just as well, cost significantly less and give you AT support once you have AT grenades.