This is a bit of a reach. Tyreek was a rookie in 2016 and Kelce was in his 3rd full season. Alex Smith had a pretty good year with Reid, Hill and Kelce just as they were getting started before being replaced by Mahomes.
I don't think Alex Smith would've won MVPs or Super Bowls in that situation, but no one is suggesting anybody could simply step in and replicate Mahomes' success. Mahomes is great, he landed in a beautiful spot and then performed at an extremely high level.