http://www.gamesindustry.biz/articles/2012-04-02-wii-u-less-powerful-than-ps3-xbox-360-developers-say
"No, it's not up to the same level as the PS3 or the 360," said one developer who's been working with the Wii U. What does that mean? "The graphics are just not as powerful," reiterated the source.
Anonymous developer
Funny thing is neogaf confirmed that wiiu actually has less shaders
"This developer is not alone in their opinion. Another developer at a major company confirmed this point of view. "Yeah, that's true. It doesn't produce graphics as well as the PS3 or the 360," said the source. "There aren't as many shaders, it's not as capable. Sure, some things are better, mostly as a result of it being a more modern design. But overall the Wii U just can't quite keep up."
http://www.eurogamer.net/articles/2012-03-26-darksiders-2-dev-wii-u-hardware-on-par-with-current-gen
"So far the hardware's been on par with what we have with the current generations. Based on what I understand, the resolution and textures and polycounts and all that stuff, we're not going to being doing anything to up-rez the game, but we'll take advantage of the controller for sure."
http://www.nintendolife.com/news/2013/09/developer_interview_black_forest_games_on_bringing_giana_sisters_twisted_dreams_to_wii_u
""Overall the hardware itself is slightly faster than the other current-gen consoles.
"Then we started working on the port, we already had our game released on the X360, and going from a console release to Wii U is easier since the consoles have very similar performance characteristics"
http://mynintendonews.com/2013/05/17/ea-senior-engineer-the-wii-u-is-crap-less-powerful-than-an-xbox-360/
EA SENIOR ENGINEER: ‘THE WII U IS CRAP, LESS POWERFUL THAN AN XBOX 360′
Essay Pro