Smith does put a lid on the offense. He's not without his positives, like rarely turning the ball over, but he is cautious to a fault, and it limits the offense. He prioritizes taking care of the ball over taking advantage of opportunities. Yes, he'll have stretches where he does take some chances, but he inevitably reverts back to the mean.
He threw just under a quarter of his passes behind the line of scrimmage last year, the highest proportion in the league, and no qb had a higher percentage of their yardage come from screen passes. The offense has been powered by a strong running game and, thanks to Reid's scheming, YAC. Well over half of Smith's yards came after the catch, again, the highest in the league. This is because he cannot operate as a normal qb.
You can say he works within the confines of the offense, but he is the reason the offense is confined.
This isn't even a contrarian viewpoint. Why do you think the chiefs traded into the top 10 to select a gunslinging qb that is the antithesis of Smith?