I will tell you this, it was a hell of a lot better than Belichick's was without Brady. But when we mentioned that during the Belichick to Dallas days we were told we don't know football.
Reid (without Mahomes): 171-120 (19 seasons, 16 winning seasons, 13 playoff appearances, 5 championship appearances, 1 Super Bowl appearance).
Belichick (without Brady): 81-100 (11 seasons, 3 winning seasons, 3 playoff appearances) - this includes the Matt Cassel season.
But yes, just like with Belichick and Brady, Reid's got better after Mahomes showed up.
Edit: The above comments about Belichick above were not meant to insinuate he was not a good coach, just that both a good coach and QB is what really matters to be that dominant, and that it was highly doubtful he would have had nearly the same success here.