The only agreed upon "rules" are what the legislature passes. "Norms" don't really mean much; those are just glorified pinky promises.
You're basically comparing "norms" to laws, but those two are not the same. The fact that there are 9 justices on the Supreme Court isn't a norm that we all just shake hands and agree on, it's what's currently set by legislation. Mitch McConnell never violated any law, nor did he change the rules via legislation. He (and the GOP) exercised the power to advise and consent (or not) to a nomination. If the people had wanted the kind of nomination he refused to consent to, they would have voted for a different Chief Executive, and a different Senate. But alas, that did not happen; those are the rules of the game.
What you (and the so called "academics") are advocating for is changing the rules of the game. Notwithstanding the merits of that, it is in no way comparable to just playing hardball by the existing rules, and to argue otherwise is pretty disingenuous.
So yeah, if things go well, maybe the Dems will have the balls to do what McConnell has done for 10 years which is blow up "norms" to get what they want. Especially if the far right wing SCOTUS members do things that are INCREDIBLY unpopular among normal non far right wing Americans, like kill Obamacare and healthcare for 15 million Americans, and kill abortion rights which is currently supported by a huge majority of Americans.
Essentially, your argument is it would be awful if the party that won the House, won the Senate, won the Presidency did what they wanted. That party supports policies that are incredibly popular among Americans. The other party represents terrible policies that Americans hate, like no COVID relief, banning abortion, racism (birtherism, "build the wall", "send her back"), lawlessness/anti democracy i.e. 1/6 insurrection, "hang mike pence", all of these things the average American does not want. But lets clutch our pearls when the party that WON, NOT YOURS, tries to do what is was given a mandate to do. SAD.
That’s because Kennedy was Reagan’s third try to fill that seat after Democrats blocked the first two. In late 1987, a year before the election, Patrick Leahy gave Kennedy an ultimatum that if Senate Democrats didn’t like the next appointment, they’d hold the seat open until after the 1988 election. That was against a vastly more popular President than Obama—Reagan had won his election in 1984 by 18 points.