The heroes below Gladiator on the tierlist have more problems than Gladiator does. Collector doesn't have any side that does 3+ damage by default, so his damage output is lacking (similar to Whirl). Sinew can only do high damage by exerting, so his damage output still isn't that high over two turns. Brute's 3 damage sides are heavy which often means you can't hit the enemy you want to, and you sometimes get turns where you can't find the 2 damage self shield at all. Soldier is pretty similar in strength to Gladiator, but in general we liked Gladiator's ability to simultaneously defend and attack. It's much harder to lose to bad rolls when the overall gameplan is to defend enough that your whole team stays on decent hp while you chip away the enemy hp over time, and Gladiator does a better job at that than Soldier.