Not weaker, just very different. The PS3, in the right hands, can be a powerhouse of a system but there are very few developers that develop for SMP systems well. Extremely difficult to moderately well, although libraries late in the PS3 life simplified this somewhat. Compared to the XB360, in the end, they were essentially comparably performing systems.
The PS3 CELL processor was an extremely elegant, exotic architecture that was designed to be scalable in connected systems. The XB360 was a more straightforward design, not as efficient, but made up for it in software (only two tape outs before going into FCS).
As for the WiiU, it is a very straightforward design that, admittedly (and obviously), has raw performance issues vs the PS4 and XBone. However, and again, in the right hands, the WiiU can produce some amazingly beautiful games that perform wonderfully. Anyone that thinks that SMW3D does not look wonderful is just fooling themselves or arguing for the sake of arguing.
See it in motion (and, for that matter, Journey, Bayonetta 2, Drive Club, etc.) before screaming about how you think it looks like crap. You may not like the art style, you may be tired of Mario, you may have a fondness for other platforms, but to say that it is bad looking? Come on....
And there is som much happening on the screen, in HUGE set pieces, that if a lack of anti-aliasing is the primary concern, then it is truly a forest for the trees issue...