But why would you want to do something strictly inferior, even if you're not doing content that requires it? If you can do 1200 DPS with one build, and 1000 with another, why would you choose the one that does 1000? Regardless of the content you're doing, you'll do better using the 'cookie cutter' build, and so why would you want to do less?
I've never understood this argument--the vast majority of actual 'game' in MMOs is about improving and maximizing your damage output, and, for tanks, learning how to maximize defensive CD use to mitigate as much damage as possible, and for healers maximizing healing output without overhealing or running dry on MP (and DPSing when possible).
Not doing that in an MMO is like, I don't know, playing a fighting game and never graduating past button mashing. Sure it might be fun for awhile, but I've never understood how it can be fun continuously.
And THAT is why raiding meta tends to trickle down into the playerbase at large, and things like str tanks aren't just for the people pushing hardcore content anymore, but a thing that most of the player base recognizes as better, and why healer DPS isn't just for raids, but something that is becoming expected. Because pushing the envelope and doing as well as you possibly can is part of the fun for a majority of people, and I just don't see where playing any game repeatedly for months or years on end can be fun in the slightest if you AREN'T doing that, regardless of the content you're doing it in.
I also don't HAVE to buy eso gear. Upgraded law is good enough to clear any of the current content. I don't HAVE to put all my attribute points into str as melee dps or mind as healer or int as magic dps, etc. I could load up on piety as a black mage. It'd be considerably less effective, but I COULD do it, and, hey, it'd even slightly change my play style as I'd be able to maintain astral fire longer! But no one does that! Because it's worse! And no one wants to be worse.
And given that, I'll never understand why 'you don't HAVE to use the mathematically best build unless you're a top raider' is an argument. It's simply not. The majority of people will do what's mathematically best not because they 'have' to, but because their goal is to be the best players they can be--as it should be--and in following that goal there is no 'choice'. Which makes things like skill trees nothing but a meaningless waste of time--both player and dev--as it only exists for people to click the button they were going to click anyway because it's the mathematically superior button.