My melee guys are lvl 12 or so and there is a skill that deals like 1000 damage up to 2000 if you count criticals.
And that is WITHOUT Rage and Oath. With Rage and Oath (+100% damage) it doubles. With Rage+Oath+Bully it's 150% damage on a knocked down/slowed/cripple opponent.
Whirlwind also plows through entire groups; try casting mass slow/knockdown on a crowd then Ram+WW them with your melee w/ bully, it's AoE oneshot.
As for being vulnerable to your own damage fields it's just a matter of planning/thinking out your strat. When you start combat, first you artillery them with your mage/archer and put your meleers on reserve to build up AP, in the second turn you buff the melees (Bless, Oath, Rage, etc) and BAM BOOM BIFF BARF KABOOM TEN THOUSAND DAMAGE ENEMY WIPED OFF THE CHARTS.
They also have an heal that basically heals 80% of your life.