I can see both sides of debates. I'm still intrigued by a mojo 3 for fun on switchbacks.
It should be noted that the plus factor on 27.5's is already pretty much doa. (Except for true fat bikes)What we are really talking about is 2.6-2.8 tires on 35mm wide wheels. This puts about an inch delta between 29'r and 27.5 "mid-plus"
to get that geo to work, you have to run a 3.0 tire to get the height that works with the 29" wheel. What the industry didn't get right is that riders have not warmed up to 3.0 tires for a number of reasons However, once you reduce the tire to 2.8 the height of the tire drops so much that your bb is effectively about an inch lower. Since modern BB geo is typically 13-13.5 you can see that wont work