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 on average are .500 or better.
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.