I am sure that he would likely make more money at U of I with NIL compared to where he would likely be drafted, but I would be very surprised if he went completely undrafted especially since smaller rookie receivers have made immediate impacts this year.
Look at Jordan Addison and Zay Flowers. I know IW is not a first round talent or even day two, but what is so different between what he could do and someone like Jayden Reed? Reed was a second round pick and has thrived in his slot receiver role in Green Bay. They are similar size and Reed never had as much production as Williams did.
The biggest thing I think Williams could do to prove himself more at the college level is ball security obviously, including making more contested catches.