The challenge he's going to have is the fact that the rest of the Conference is starting to improve and it's not quite as diluted talent-wise as it was just a couple of years ago. When you look at teams like Cincinnati, Buffalo, Baltimore, (heck, even Jacksonville) etc. each slowly starting to rise, they'll all present potential speed bumps during the regular season and also possibly even play the role of spoiler in January. Then add in potentially Vegas (with Garoppolo), the Chargers, and possibly Denver (if Payton can turn that around), and even within their division, it's going to be tough.
Mahomes is a solid player, but unless he dials it back and starts playing more within himself and stops putting himself in harm's way, the lack of longevity may also be what holds him back. I've said this before, but he and Reid connected at the wrong time for a long run. Belichick was a lot younger when Brady got here. Reid is 65 and isn't anywhere close to in the same shape as Belichick, so coaching later into his 70s doesn't feel as likely.