27.5" wheels vs. 29'er on descends and muddy roads.

I've been riding several 29", 27.5" and 26" wheels on mountain bikes and I just don't see any advantage of the "big wheel". I'm not saying they don't make sense, but I am definitely saying this: if you have a decent, old mountain bikes, don't buy a new one thinking you're gonna be faster. That's it!
Bike on this video is the ‪@MERIDABIKES-INT‬ Ninety-Six from 2014.