Who wants a knuckle sandwich? I dropped almost all my levels in attack, and it generally saved me the fuss of reviving. The displayed damage numbers don't increase with level, but punches do "feel heavier."
Heroic charge is when you chain a long enough combo of cleared tiles. If your horseman and knight are taking too much damage, give them weapons/armor with block chance or use more damage-abilities to get the jump on your enemy waves.