All things considered I think they do a pretty damn decent job at balancing. Yeah, it's not perfect and there's always issues - But for the amount of systems that they have to work with it's a miracle it's not worse.
Outside of PvP it's very rarely as bad as people make it out to be, and even PvP really only feels the effects because of PvE systems for the most part (trinkets, corruption, essences). Obviously there are tonnes of examples of totally busted PvP moments (Like tanks in arena), but that's typically the exception and not the rule, the better team still generally tends to win when all else is equal.