Weakest system of the 3? Pfft, no other 5th gen system game can touch the size and scope of Morrowind.
I said it had the weakest *library*, which obviously is somewhat subjective. Horsepower-wise it was probably the most capable of the three systems, that's not in question.
Can't argue PS2, but I'd definitely argue that Xbox's library is better than GameCube and Dreamcast's.
I would also pick the Box over Dreamcast. But over the Cube? Not even close. The only reason the Cube is looked down upon is the fallacy that is the N64 breathing its disease over its replacement. But that wasnt even enough to stop the little box. It has probably the best Zelda library of any console system for starters. That alone will topple anything but the PS2 by itself. If it wasnt for the fact that the PS2 was B/C, it would be arguably the best system of that generation.
I like my GameCube, I love first-party Nintendo games. No hating on it here. But the Xbox had it's fair share of good first-party games, too. The difference with Xbox, though, is that it had strong third-party support, as well, which GameCube lacked.