First off, /wave Faille, it's been ages and ages since FFXI.
Second, as much as they initially screwed up with GU4, it honestly did not make raiding impossible. My guild on Xeth continued killing the same shit we had previously when buffs were dropping and we were lagging and have progressed on mobs that they "fixed" such as Shylosia.
As someone who started off in beta as well, Vanguard definitely has come a long way. As has been mentioned previously they've fixed many classes and have the remaining classes slated for fixes. Hitching and framerates have seen significant improvements and they've fixed a lot of game play.
Don't get me wrong, there's still plenty wrong with Vanguard and they've made some pretty boneheaded design decisions (G4 loot paramount among them). But when you compare the game as it was at launch with as it is now, there is a huge difference, and the culmative difference is positive.