Interesting fight. Pyfer hits way harder and has a reach advantage, but his stand-up really isn't that good on a technical basis. Alhassan was working him with kicks at range and forced him to grapple his way to victory and Hermansson also outstruck him for the vast majority of their fight.
Gastelum is the more talented and well-rounded striker with a fantastic chin. He's gone the distance with dudes like Cannonier, Izzy, Rob, Prime Woodley... he might actually be able to take Joe's best shots. But he isn't getting any younger and we've seen him get hurt before.
I'm also intrigued by how the grappling exchanges will play out. Joe intrigued me by showing that he could pull takedowns and a decent top game out of his back pocket against Alhassan. He's also looked good in several no-gi matches... but Jack showed him levels.
Given Gastelum's lackluster defensive grappling, it's not out of the question that a big strong dude like Pyfer could outmuscle him and mix in some TDs/ground control. Likewise, Kelvin often mixes in some takedowns of his own... he'll be at a size disadvantage, but his entries are good and we've seen Pyfer get put on his back and outscrambled before.