Brute Force and Total Carnage do not stack, otherwise there would be an increase of the hitting power of the gladiator who has them with every hit. They may be flat bonuses, they may be percentage bonuses but they don't add extra value with time.
Frankly I don't understand that comparison between Rampage, DFA and KO. The first two obviously don't win the fight if the dice rolls in your favour, can be deflected, can be disabled by Create Distance, can be taken out by knockdowns (the latter doesn't even apply to KO), have cooldowns. In other words - they are completely normal skills that help your gladiator fight better, not win more by default.