I see your point, but imo even though Kelvin's loss to My Boy was less than a year ago, he has distanced himself from that loss with 2 consecutive wins. One over the former champion and the other over a dangerous top 5 contender who for sure has a better submission game than My Boy, which hints that maybe Kelvin improved in that area after the loss.
If you look at My Boy's win streak before the loss to Rockhold, its mostly against ageing, past prime competition. Souza and Kennedy are imo better wins than any from My Boy's streak.
Plus, if it really is a 50/50 toss up for the next shot, why not reward the dude who moved up despite being small for the weight class and performed better than most expected him to. Put some fresh blood in the title picture.