WoW did try to solve a lot of what was wrong with MMO's back then, much in the same way as GW2 does now. In MMO's before WoW, kill stealing was even more prevalent because the one that did most damage to the target got the kill. Also the main way of leveling up was simply mob grinding, there were hardly any quests and if there were they didnt give a significant amount of xp, or non at all. WoW introduced tagging (the one that starts the attack gets the kill and loot, no matter who joins in later) and introduced mainly quest based leveling as opposed to grinding mobs all day.
Yes WoW got old and yes some have never liked it, but there is a significant amount that did, including me. I still like it, even if it is for mostly nostalgic reasons now. Thank god games develop and react to new situations/wishes, doesnt mean we have to point at older games as if being old and outdated is actually a flaw. I am sure that if you asked Blizz they would never have expected to do so well as they did, I don't blame them for not significantly changing a winning formula. Maybe they will with Titan, who knows?