Mahomes basically started in his 2nd year in the league after getting to sit a year and learn with the offensive mind of Andy Reid as his HC. Also when he started he had Hill and Kelce as well as a competent O-line. Josh on the other hand started his rookie year none of the WRs/TEs that started with him would make it really into the next season most wouldn't even start for another team the exception being Zay Jones who got traded in October of the 2nd season, and I'm pretty sure he lost his starting job before he figured things out with the Jaguars. His O-line that rookie year same thing none on the team or starting anywhere else the next season with the exception of Dawkins.
So that first year might have been a bit different.