SDE heroes are in no way balanced or even playtested to be balanced. There is wide disparity in quality of heroes.
In games like this where there is no expectation of balance, 'tiers' are born and you either self-censor by choosing to ban OP heroes or choose to stick with 'all low tier' heroes or accept it as-is.
Same with monsters. Some spawns are stronger than others, and some combos are even stronger. The game isn't actually fair or competitive. It is a experience system, enjoy the ride and the destination is meaningless.
This is complete nonsense. While there are some heroes and monsters that may be considered more powerful (or more accurately some are very good in certain combinations) often it is a case of learning how to use those heroes/monsters most effectively. The game is well balanced, fair and competitive.