Are there actually people who want a "playoff cap" who don't also believe Kucherov was deliberately held out? Because this is a fundamental disagreement with the cap being calculated as a pro-rated sum of daily cap hits for the entirety of the regular season. The cap has been around for 15-20 years, and I don't recall ever seeing people advocate for preventing teams from ever rostering a team whose summed cap hits exceed the cap, even for a short period. This would kill the trade deadline, and disincentivize teams from adding meaningful replacements for long term injuries.
My impression is that the entire debate about the cap started this year, from a conspiracy theory about TB's handling of Kucherov. Is anyone complaining that Boston was "over the cap" because of the Taylor Hall addition?