Except the actual MMO depicted in SAO fucking sucks. Like, once you remove the whole "Oh my God it's like I'm really there" hyper-advanced simsense VR aspect, it's a really shitty game. The only possible builds are DPS and Tank, there's no magic, no ranged, nothing to make stealth viable. You can go into crafting but that's about it for any other skills. The whole "unique skill" mechanic is basically just pure "Fuck you" RNG and would be impossible to balance. Loot gets handed out based on last hits so fuck cooperation. It's a mess. If you made an MMO with modern tech that perfectly recreated the mechanics of SAO, no one would play it.