Obama didn't refuse to seat a justice, he was blocked by Mitch McConnell. Who also blocked every single judge appointment that Obama should have been able to make in the last 2 years of his presidency. And Republicans were talking about leaving that seat open until a Republican won the presidency. This is why trump has the most judicial appointments of any president.

And RBG reduced to retire likely out of pride during the Obama years, but smartly didn't retire during the trump years.

Biden refusing to stack the courts is pretty shitty, but if he does so it's going to open the flood gates for that being a possibility. Do I think he should? Yes. But I also think that if he does so their should be a cap put in place, but to put a cap in place would require a constitutional amendment, and there's no way that will get through our current Senate.