Those are problems of the building not Penals
But the anti building tool that PG do not have.
Its called PTRS
They have good vet bonuses that are superior to Panzerfüsilier up to vet 2 and inline with them at vet 3.
PTRS is not a weapon upgrade, it's a mediocre sidegrade.
Saying all these things are just a problem of the tier building and not Penals themselves is true but I can't build Penals in other tier buildings so what is the point? Penals do have these drawbacks and there is no denying that. Only way to solve them is by going for a doctrine with dhsk/m42. It's simply not possible to get 3 Penals + T2 + Zis/Maxim as you will never have enough MP unless it's a complete noob stomp.