Masvidal was a giant LW and was definitely killing himself to make weight.
He had absolutely no problem fighting Mutante, Larkin and Maia, all former middleweights.
Wonderboy has a big frame for welterweight, and he's got great range, but he isn't up there in regards to physicality. Matt Brown straight up prison mauled him by being more physical. Woodley obviously was far stronger and more physical in grappling exchanges.
Wonderboy presents a lot of problems for guys by being able to hit you with his lead leg with zero notice, and some really dynamic spinning attacks. His hands are competent but nothing to write home about. His kicking game is incredible.
For his part, Masvidal never gets out classed on the feet. He's been striking his entire life, arguably rolls with punches better than anyone in any division and is still very athletic with excellent timing.
If Masvidal loses its going to be his very typical problem - bad fight IQ. Don't get me wrong, he actually has INCREDIBLE fight IQ, he just doesn't always employ it. Sometimes he plays tit-for-tat if you landed something, and we all know he's had a problem with coasting when he's won some rounds.