Nah, the GC was actually in a tossup with the Xbox for most powerful console of the gen, while the Wii U is a gen behind. And for all the talk about Nintendo's lack of 3rd party support over the past few gens, the GC received a pretty good share of 3rd party games, many of which were superior to the PS2 versions in terms of visuals.
I'm just curious here, but can you give me like a dozen or so examples where this were the case between 2001-2004? Because to my understanding GC versions of multi-platform games were almost always deemed the worst of the pack. Even Sonic Adventure 2 took a performance hit on the Gamecube, a port of a freaking Dreamcast game.
Games like Resident Evil 4, for example:
1) Well for a start, the game was actually lead developed on the Gamecube rather than the usual vice-versa. Developers usually started on either on the PS2 or original Xbox and ported to others accordingly.
2) I said 2001-2004 for a reason. The damage was already done by the time RE4 was released.