I wouldn't call Xbox 360 weaker than Wii U. Less modern, sure, but Wii U isn't as powerful, overall.
http://www.gamesindustry.biz/articl...ess-powerful-than-ps3-xbox-360-developers-say
IIRC the Latte GPU has 160 shader ALUs whereas the Xenos GPU has 240 shader ALUs within the 48 shader units.
The Expresso CPU is clocked far lower than 360's Xenon CPU. Each use different PowerPC architectures, even though both have 3 cores.
Main memory bandwidth of Xbox 360 was 22.4 GB/sec and Wii U's bandwidth is only 12.8 GB/sec. Both GPUs have higher speed eDRAM / EDRAM to ease the bandwidth limitations of the main memory.
Wii U's main advantages over Xbox 360 is the more modern, more efficient GPU and double the RAM (for games).