I think there's an issue on your question. Personally I find them balanced, but wouldn't that make them usable I'm competitive terms? Imo not really.
Considering that they pack S5 (7), PF and scaly skin 4+ I think their price is fine. I don't consider them to be overpriced. The issue come from how great weapons work meaning that they rely on getting flank charges, not to mention their limite role in general. Besides they aren't ideal targets for augments, besides + To Hit spells.
Strictly competitively speaking you'd want the most efficient unit. In our case that would be our characters they are faster, have more attacks each model, higher chance of hitting and vastly more defensive. Not to mention their multiple purpose role.
So again I do find kroxigors to be good and balanced, but unfortunately for them, strictly competitively speaking we have cowboys as the better alternative.
Could they work in casual/friendly environment (=not min/max builds? Yeah I Very much think so.
Anyway with that said I think they're very hard to change. We cannot possibly give them stuff like 5+ regen. It would be nice, but that would make them way too powerful for what we pay and what we pay for is the unique option to take a S7 monstrous infantry unit that can potentially generate more attacks.
What would make them better? Giving PF to second rank and allowing the dumb troglodon to use its roar on all friendly models across the entire board every round. Or within 12" lol.
I think with kroxigors we need to look at maximising their damage output because that's what they are. Also fluff wise it wouldn't make sense to give them +3 scaly skin.
Personally I find the models, with the exception of PF as mentioned, to be near perfect. Do remember that our book is very well balanced, however, it's because we're up against super ridiculousness such as warrior of chaos in general, elfs and especially white lions etc. A lot of the armies have overpowered must have units and you can complain all you like, but our book wasn't made like that. The biggest fvck-up is the troglodon and to a degree nerfing CoRs.