The WiiU is a fair amount stronger than the current gen, but "light years ahead" is a gross exaggeration. I don't think even the PS4 and Xbone could justify that description P:
The WiiU's biggest problem (graphically) is Nintendo's lack of HD experience. First parties tend to be the primary pushers of their consoles graphics, and it's unlikely we will see Nintendo themselves pushing standards much past frame rate and resolution, which is totally fine for the kind of games they make. Just don't expect the WiiU to be jumping leaps and bounds ahead of the PS360 for a while (i'd say the next proper zelda game has a chance, but it's a while away).
The best looking game I've seen from the WiiU thus far is Monolith's X. Past resolution it doesn't look that far ahead of Final Fantasy XIII, which came out in Japan nearly 4 years ago :/
Anyway, anyone who doesn't think the WiiU could run GTA5 is naive.