I don’t think SC has as much wiggle room to justify a squash attempt under 1965 HEA, the law is written very plainly there.
You’re right about executive overreach though, Biden would have to rally his congress to resize the court. He could have leveraged the majority activists handed him via GA in his first 2 years to do this. And when certain scumbag senators refuse to play ball, campaign aggressively in their home districts against them - whatever he has to do to fight for us. Which he isn’t going to do at all.