I think you're both right and wrong. The reason the Wii-U is about as powerful as a 360 is that 25-30% of the processor is dedicated to the tablet controller. So even though the hardware is superior... it looks about the same. Now it's a question of whether that strategy was worth it. It kinda makes sense for 2013, 360/PS3/Wii-U will all have the same horsepower for developers for the main game. Then they add on as much content as they can for the controller. But in 2014 when everybody is making games for PS4 and XBox720, the Wii-U becomes underpowered again like the Wii for the PS3/360 and probably a bit of a pain to support.
This is true, but the scenario has changed a bit. The Wii was stuck at 480p and low quality textures while the 360 and PS3 were running 720p with mid grade textures. This time around, the Wii U is doing HD and will be able to display mid to high quality textures. The PS4 and 720 will be displaying at 1080p and mid to high quality textures. This plays a lot better for Nintendo, because they're going to be displaying HD even if it's not 1080p. Also, if the game is running 1080p on the PS4/720, it should be portable to the Wii U in 720p if they disable some lighting/shadow/environmental effects.
Will the Wii U be weaker than the PS4/720? You bet. But it will still look good and third parties will be able to port titles to it without totally rewriting the game like they had to with the Wii. And, for families that want Nintendo first party games and can't afford 2-3 consoles, it will probably prove to be the best value, especially depending on the price of the PS4/720. Then again, if the 720 manages to launch in the $300 range...things could get interesting.