People like to defend the Wii U because it is the fragile small ugly kid. The other ones can defend themselves. That's why they point other consoles, to not hurt the feelings of the kiddo.
Wii U, it was just stupid on Nintendo's part to make GameCube ideas the core of the system while the software library took a similar direction. At least it got some good 2D platformers, unlike the barren GC. What makes the Wii U so disappointing is that Nintendo should have known better. The GC was just the next step on a continued decline, but the Wii U came right after Nintendo's most successful home console. Wii U also managed to surpass the N64's dreadful software droughts and that was not an easy feat.
That's pretty much it in a nutshell.
I also think the people who think more highly of GameCube don't quite remember the period accurately. It was a system filled with derivative titles, poor design choices, and inferior ports missing features and content.
I describe myself as a little dose of toxic masculinity.