I went three, but it could be any number on that list and it wouldn't shock me, though anything above 4 would be incredible. He's an amazing talent: I think a small handful of QBs in their primes could put up Mahomes numbers with his offense but it's a small number. I think most great NFL QBs do worse than he did last night with the pressure on him (like that was worse than Brady/Giants) and his receivers let him down. However, beyond the sheer difficulty of winning a Super Bowl, there's a lot of yellow flags. He took some hits last night that most QBs wouldn't have because they wouldn't be running around like a crazy person to buy his WRs one more second. That hit with JPP/Suh/White (I think) last night was terrifying and in these playoffs he was knocked out a couple other times. He doesn't have a decorated injury history but one or two more concussions or another knee/foot injury could hamper his potential a ton. I also think he's been fortunate to work with the offensive talent he has. Kelce and Hill are all-pro talents, Hill's one of a few WRs who requires a defense to work around him, and he had a lot of rawer pieces around him with good skillsets. I wonder what that will look like when the salary cap crunch comes into play and KC needs to make decisions that either require him to rely on less transcendent talents or make him put up 40 a game because the D isn't there.
I've just noticed he often works himself out of jams by scrambling for seven seconds and hitting a WR who finally broke away from their coverage. The time in pocket splits back this up: anything over 2.5 seconds in the pocket he throws a lot deeper, is more prone to interceptions, and his completion rate plummets. He's still great, just a different QB. I don't know if that continues if you don't have Kelce and Hill being the targets in those scenarios. At some point that'll bite him or his scrambling will become less effective. I also wonder how he'll adjust as, inevitably, different offenses come into play. Last night was noticeable as, despite being down three scores, they were huddling up and running 20 seconds off the clock between plays. That led me to look at his splits (since PFR has tracked them for Brady, so not complete)
Of his 1618 passing attempts, 34 were no huddle and 165 were under the center. He is spending 90% of his time in the shotgun and 98% of his time in huddles on passing plays. Over 10% of Brady's passes were in no-huddle over his career (with small degradation stat wise) and about 70% in shotgun. I'm not super concerned about huddle/shot-gun, but we've seen that Brady has won a few super bowls due to his ability to be deadly in a no-huddle. It feels like he should be even more dangerous in a no-huddle but the severe reticence to run it is a little concerning to me, especially with the meh results doing it thus far. I spot checked a handful of prominent NFL QBs and the lowest number in terms of no-huddle I could find otherwise was 6% with Lamar Jackson. Most others range from 8-14% or so. Russell Wilson is probably the best comparison: mobile QB with a rocket arm who ran no huddle about 4-5% of the time, so it's not a true hindrance but I think worth noting. Russell has also dealt with garbage O-Lines and great WR talent and hasn't made it back to the SB since a tough loss to Brady. Kyler Murray just runs no-huddle for fun but nearly everyone else is in that 8-14% range in terms of top QBs.
I think he's the best QB in football and has plenty of talent around him right now. If anyone is going to win 3+ beyond Brady that is currently playing it's probably him, but it's a big ask and I still think the jury is out on whether he can adjust himself to different talent types over the years as Brady (and Rodgers, Manning, etc.) did and, if so, what that looks like. We saw last night what a collapsing line does: it forces him to scramble and make miracle pass attempts.
Edit: To be clear, I don't think any QB wins that game last night at QB with that line play. I do think Mahomes play style, KC's vertical offense, and the like really emphasized that there is a weakness there though. I was consistently surprised at the lack of screen plays, short passes, running back passes, etc. as the game went on.