ACP should be reduced by Str bonus. So a -4 ACP should be reduced to 0 with a Str of 18. Strong characters should be strong.
Move penalties have no purpose and should be removed.
Heavier armor could increase the crit DC: with medium armor an attack is a crit only if the roll is AC+11, with heavy armor it requires a roll of AC+12. Not sure this would do anything if they reduce the stats of the monsters. And maybe it would be too complicated to have 4 AC values ("AC 20, TAC 17, crit AC 32, crit TAC 27 or 29 I dunno?"). Anyway, if the monsters' damages stay as swingy as they are now, heavy armors could be a way to reduce the swingyness; in term of "verisimilitude", add some fluff like "heavy armors don't significantly reduce the amount of hit you suffer - some blow are deflected, but your dodges are less efficient - , but they reduce significantly the amount of *deadly* blows" and call it a day.
This is a fantastic solution and would basically solve all of my issues with heavy armor at the moment. It's logical from both a realism and a game balance perspective.
You could even keep in move penalties for characters with Str <15 or something and I'd be OK with that, if the rest of this was implemented.