Goliath brawler with calm + power weapon + slaught = infinite attacks for just 22 starting AP within MP range. Add order planning + joltseed and that can be up to 109 MP for 37 AP total. Pretty easy to get 5-10 kills by 1 player at the start of the 2nd round vs AI.
Limiting them to once per turn can help. Free repair/reload usually means 1 extra attack for your turn which alone is powerful. I'd almost think that 2x per mission might even be preferred, 2 total only 1 per round.