The thing is we need a larger Supreme Court, mostly to ensure more throughput. Have, say, 21 justices with most cases having 7 justices presiding would do wonders for Supreme Court backlog. If it is something major, then call in the entire 21 Justices.
That defeats half the purpose of having a Supreme Court. Anything that is important enough to reach SCOTUS is important enough that it should already be heard by the whole of the Court, not by a panel of justices. That also makes the law subject to luck of the draw and causes issues with precedent.
As for SCOTUS being enlarged, while I probably would have gone with 13 Justices as opposed to 9 if startings from scratch, it is politically impossible. At a minimum you would need majorities in both the House and Senate while also holding the White House, and realistically you would need commanding majorities along with broad popular support or the backlash come the next election would be
epic. If the Democrats tried it, you would immediately see massive campaigns to fill the state legislatures for the purpose of ramming through a Constitutional Amendment that strips the additional appointees of their positions (and maybe voids all decisions that they were a party too) and fixes the size of the court at 9. If the Republicans tried it the Democrats would run on impeaching the extra justices and replacing them; and are liable to win.
Also, have some sort of provision to ensure that the seats are filled within a year of a retirement/death/removal of supreme justice(s), just to prevent what McConnell did and anyone else trying that sort of shit again.
Nah, SCOTUS is already the least timely branch of government. Keeping the odd seat empty when the stars align really isn't that big a deal. And the Justices are powerful enough (and serve for life) that no one should get to default into the role.
Garland couldn't get a majority of Senators to support him. If he could have, McConnell never could have refused to hold hearings or do anything about it. All McConnell did was provide political cover to the Republican Senators and shift the conversation happening nationally to one that was more in favor of the GOP.
Voting against Garland would be hard on the merits for a great many vulnerable Republicans and holding hearings, and then having a vote, is going to make the Republicans look bad when they vote against him. It also makes the attack ads easier. On the other hand, by not holding a vote McConnell enrages the Democrats and essentially forces them into broad attacks on the GOP as opposed to specific attacks on specific individuals and focuses a lot of the anger on him as an individual.
There was also the secondary advantage of doing nothing with Garland as opposed to rejecting him. If Clinton won in 2016 (or Republicans lost the Senate) then the day after election day, Garland would have suddenly had a hearing and been approved in record time. Garland was the best the Republicans could hope for from a Democrat President, and both Obama & Hillary (and the Democrats in general) spent far too long touting Garland as supremely qualified and a great choice; pulling him simply because Hillary won wouldn't have been politically viable.
This is actually easily doable compared to passing a Constitutional amendment since Congress sets the size of SOCTUS as per the constitution. Of course they haven't change the size since 1869 but they do have the power.
And if it was even seriously suggested, the Republicans would run on passing a Constitutional Amendment to fix the size of SCOTUS at 9.
As a practical matter, court packing is politically suicidal for both sides. Honestly, it wouldn't surprise me to see such an Amendment floated in the next few terms anyways; simply because packing the courts has been again suggested by the Democrats when they don't like how it is ruling.
Partially because the Supreme Court's power is actually precarious at the end of the day. It only has power by either having Congress or POTUS at their back. If neither supports it then the power it has is gone.
No, their power rests on popular support and legitimacy.