Of course the Switch is faster in the vast portions of many games compared to the WII U (just about everybody acknowledges it) but you can't say that it means NOTHING in a conclusion when we have sources like Digital Foundry to brief us on the specifics when they conduct these comparisons ...
Did you actualy read what I wrote!?
Again, fact that this game runs at 648p in portable mode compared to 720p on Wii U dont mean that Switch is less powerful than Switch, (esapcily beacuse MK8D that definatly look more demanding is 720p in portable mode), Digital Foundry in Resetera thread said that's possible that Nintendo done that to increase battery life for game. Also onother strange example is Bayonetta on Switch, it runs at 720p in portable and docked mode, and offocurse that Switch in docked mode could run Bayonetta at higher resolution. Also have on mind that when you porting game designed specifically for totally different type of hardware, you want have best results in any case. So no, you cant use one specifk game as a benchmark for Switch's undocked mode.