Monster Hunter has... i think 18 weapon types, which all also need extensive testing against all sorts of monsters in different terrains. Meaning you can get into a LOT of different scenarios, to make sure none of them feel useless.
Other games i mentioned are fricking long in playlength, meaning you need to test like 100+ hours for a casual playthrough, which people can play differently in approach.
And what about Guild Wars or FF14? Yes, WoW has a lot more specs, but they rarely do HUGE shifts like with Survival going melee or demonology becoming all about summong minor pets and just iterate more on themselves. Most talents are existing spells, passives and abilities or returning ones, which barely need any testing.
Yes, a game like Red Dead Redemption needs different kinds of testing, but a lot of what you mention is just number tweaking and making sure stuff doesn't go into infinite loops or things like that. But there are plenty of games with FUCKTONS of content that needs to be tested, that make due without player betas. And just because it's "WoW tradition", doesn't mean it's a good tradition. At this point, the game always gets "solved" before it even launches, be it patches or expansions and you get insulted when you set foot in a raid the day it opens and don't already know all bosses in and out (although a lot of that is a playerbase issue)