Again regardless of their performance both Penal and VG they are fundamentally badly designed since they are too cost efficient for all around units leaving little room for more specialized units.
Their design and performance creates problems both in balance and diversity.
Penals, while strong, are far from the most cost-efficient infantry. You have to build a 160 mp tech building and then build every single penal for 300 MP, which means you have to play them perfectly in the early game or you will easily lose any and all map control.
They also aren't all that versatile imho, unupgraded they totally kick infantry ass, but that's only in a vaccuum with no variables involved, they have no grenades (a snail could dodge a satchel so it doesn't count) OR they get the AT package which makes them marginally useful at shooting light vehicles and snaring, but their AI capability is basically neutered and they're only good for ambushing and making opponents think twice about vehicle diving at that point.