Remember with the ps3 you have two types of memory so it effectively has 44GB/s overall. Where as I think wii u is something like 60GB/s for its edram (could be wrong) but that is only for 32MB. Anything the wii u needs outside the 32MB edram has a very low bandwidth of 12.8GB/s and remember that 12.8GB/s memory is a bank of 2GB of which 1GB is reserved for the operating system. So its less than 12.8GB/s + eDRAM.because the operating system is also accessing it. Same with ps3 but only one cell processor is used for operaitng system I think.
I honestly don't know how either ps3 or 360 would handle xenoblade but I suspect it would be a lot better than you realise properly programmed. Somethings would be better and others worse. Xenoblade seems designed to offer impressive visuals on weak hardware by keeping textures low resolution and by omitting many normal graphic features. The original wii version and later 3DS version both work well on weak hardware.
