Have you even taken a look at the stats of grens and other line infantry? Grens have excellent stats, and they scale really well with vet.
There is abosolutely NO reason to add a 5th man on grens or increase HP/model...
Keeping grens alive in lategame a pain, they die to AoE so damn fast.
In 2's this is really horrendous, where lategame ost consists of nothing but armor and a train of pio's.
have the last tier give a +2hp bonus to every ost 4 men squad, except for pioneer.
They make them more resistant to wipe without needing to balance having a fifth man.
increaseing hp by 2 also means that every infantry force needs another shot to kill grens.
Bulletins that did the same got removed for a good reason.