Gamecube was definitely more powerful than PS2 but its GPU had one outdated quirk.

It was using the Texture Environment Unit, which was able to combine 8 textures and do next gen effects like bump maps or reflection.

However it was a completely fixed function pipeline so developers couldn't write their own custom lighting or scale it as game engines got more advanced. It's why even games on the Wii still looked a bit uglier than the original Xbox, even with the faster clockspeeds.