I think it's way too earlier in Mahomes career to make any kind of long term assessments, good or bad. He played great for most of last year and has a lot of potential.
That's about all I'm willing to say at the moment.
This right here is my point entirely. As a reminder, here are the QBs under 30 who were above average in passer rating last year:
Mahomes, Watson (good but on the Texans, so..), Wentz (two injuries in two years is a big warning sign), Goff (is that his name, or the sound he's making while choking?), Luck (will be 30 next season), Prescott (barely above average). That's it.
I'm not saying he will be the next Brady. If he were it would be great for the NFL, but first I don't think that's likely at all, no one will be, and second it's entirely besides the point.
I do want to take a quick aside to address the points made about Prescott, Luck, and some others with huge expectations placed upon them after great opening seasons. First obviously the seasons which led to those expectations were not comparable, but in part that can be explained away with rules changes sure. Not in whole, but in part definitely.
Second, indeed, most QBs suffer a "sophomore slump". Prescott is actually the perfect example. His rookie year he had a passer rating of like 105. His next year it was 87, so it went from exceptional, to below average. However the next year, this year, it rebounded to 97. He went from exceptional, to below average, to above average.
That pattern (the second year, with tape on them, is Much worse than the first, and then they learn and adjust and things settle into somewhere between the bounds established by those high / low years) is the most common one for QBs in the NFL. But that means he would Still represent a bright spot for QBs under 30, simply because most of them are not great.
However all of that is beside the point. He doesn't Need to actually be great. He just needs to Look great at the moment, and represent exactly what Jaric said, a lot of potential. The fact that he may not actually Be great, and this year may represent a culmination of a lot of factors and he may realize he's playing way above his head actually makes it even More likely the "worst case scenario" I detailed (where he turns down a 200+ million deal which was very publicly offered, and very publicly transitions to another sport) may occur.
All he needs to do is get lucky and ball out one more year. Certainly plenty of folks have played great two years in a row, Wentz is actually a prime example of that, between last year and this, though he looks like he may not last 10 years in the NFL never mind 20. But if Mahomes DOES play amazingly next year as well (it's just one more year), and then retires, it would serve as a very visible representation of what people already fear is happening behind the scenes, a siphoning of talent and more than anything else Potential out of the NFL, and talks with folks below the college level confirm that is indeed happening, enrollment in below college football is WAY down.
Right now the NFL is 'fine' because you can convert athletes into other sports relatively easily, and the NFL has the perfect mix of huge money potential and lots of roster spots. But if it's seen very publicly that folks are starting to choose health over money, with someone providing both that example and some guidance as to which sport to switch to, I truly believe a significant portion of the viewers would switch as well.
And the equivalents given by others are not really equivalent. Sanders quit because he was on the Lions, for example, and who could blame him? No highly visible NFL QB has turned down a 9 digit contract to play in another sport, it just hasn't happened. And as Mahomes is hyped more than anyone else right now, and just had the best 2nd year (1st as starter) in NFL history statistically speaking, he is in the prime spot to be the one to do the damage. I don't think he will turn it down, I don't think this is a particularly likely hypothetical. I'm just saying, it's not impossible, and him doing it would be more damaging than anyone else doing it, at this point in time.