I'm not criticizing because I certainly don't have the time to look into it at the moment. But this thread is full of anecdotal Pace and SRS champion cases. If anyone wanted to deep dive into Pace-regular season X Pace-playoffs X Success-in-Playoffs (not just championships) the hypothesis could be better tested.
Pace isn't the main factor causing high powered offences to dip in the playoffs though. The main driver of successful playoff offences is the ability to score reliably against a variety of coverages.This ability is usually achieved by a halfcourt maestro or a balanced team that can handle anything that playoff defences throw at them, and high paced offences might not necessarily lack that ability (see the 2015-2019 Warriors).
That's fine, but more anecdotal. I'm curious if there is something related to pace that is significant.
The Final 2 teams of the last 15 years or so have had plenty of top tier pace teams, plenty of mid-tier pace teams, and plenty of bottom tier pace teams. In other words, there really doesn't seem to be much correlation at all to pace and making the Finals. I suspect every team is less efficient and a bit slower in the post season, but that happens when you play the same team and those teams have better defenses (on the whole). It doesn't however mean that a fast paced offense is just going to collapse and die in the post-season.
At the end of the day, the more talented teams with the best players tend to win. Some of those players play a fast pace and some play a slow pace (Lebron's teams, for example, tend to be in the bottom half of the league in pace). Pace really isn't something that seems to matter at all to playing winning playoff basketball. SRS though does tend to correlate, pretty much every team in the Finals is a top tier team in that (and the champs are often top 3) with the only real exception of late being Lebron's last year in Cleveland when that team was a mess for much of the season.