Fairness in combat is in the eye of the beholder, to a certain extent. There are people who will insist a fight is unfair because one attack hits really hard even as a few dozen different hints say “move left and it won’t hit you.” But that’s the minority. Sometimes fights in MMOs genuinely are unfair, and it’s not always because the fight is just too dang hard to do; sometimes the fight is unfair because you play a melee class and getting into melee range is just not something the fight actually lets you do.
And there are other options. Maybe you’re red-green colorblind, and while the tells in this fight are theoretically clear if you weren’t, they’re absolutely opaque based on the color differences. That is unfair. So what MMO combat has felt unfair to you? Was it a specific fight? A whole game? Even just a smaller era of a larger game history?