Apart from the guys on your list who aren't even in the UFC, they definitely could get 5 in the next year or 2 with Evloev, Khamzat and Umar could get a couple more wins and would likely win a Merab rematch by sweeping the first 3 and either riding out till decision or forcing Merab to take chances he wouldn't otherwise and getting a finish.
Islam probably missed his window at WW. He would have beaten Leon, but I don't think he'd take the fight with Boolol and he's already going to be 34 in a few months and doesn't have that much time to wait it out for another champ, and certainly not long enough to win the belt and hold it for a while.