My personal argument would be the talent composition of those Chiefs rosters pre-Mahomes versus the McCarthy era Cowboys teams, which I think is night and day, but it doesn’t change the fact that it’s a decent point to be made and people can argue the merits of roster talent.
I think judging coaches on playoff records is going to have most coaches looking bad unless they are Reid with Mahomes (.842), who easily crushes Reid without Mahomes (.458). It's a matter of math.
In a 14-team playoff, 10 teams are going home with a .500 or worse playoff record. That's 71% of the entrants that are doomed to being even or worse. It's not a parity situation where half the teams can be winners.
Based on the standards I keep reading, a coach that doesn't have a winning record in the playoffs is a loser, even though most coaches in the playoffs are a favorite to be .500 or worse. Reid without Mahomes would be a bum that chokes in big moments according to a lot of people based on having a losing record in his first 24 playoff games. He has won three Super Bowls plus an AFC Championship since then.
The standard only gets more unrealistic when it's Super Bowl or bust, particularly with Mahomes and Brady dominating the Super Bowl win column in the last decade.