The "best" at what though? Because history disagrees with this statement.
That said, I can agree that it was amazing when it launched, had great potential and I still think the soul system in it is one of the best character defining/ progression systems out there.
The problem, for me, was that because of the ability to macro your core rotations the game play for nearly every class could be simplified down to just mashing a few buttons endlessly. The only role where that's not true is obviously healer due to how reactionary it is but for DPS and tanks you could just mash your core rotation macro and do respectable if not top DPS.
That and the core game play draw was Rifts....which were almost all the same and after a while just became super annoying because they disrupted the questing.
This is even before they screwed up the game by introducing one of the worst F2P models I've ever seen in a game and monetizing the shit out of everything.
I played on and off every once and a while before Storm Legion, then I got Storm Legion played for a few weeks and I don't think I've ever been back since.