“1. A GOP Senate can block every presidential appointments — notably Supreme Court justices but also cabinet appointments — indefinitely.”
Only if the GOP senators vote as a block. Unfortunately several GOP senators are notorious for being “independent”. Murkowski, Collins, Romney are prime examples. Sasse was just reelected and could defect from time to time. Burr in NC is a lame duck and is best buds with Mark Warner. He loses nothing if he breaks ranks.
If the GOP has only a majority of 1, don’t rule out a party change. Consider the example of GOP Senator Jim Jeffords in 2001. He left the party to become an independent who caucused with the Democrats thereby shifted the Senate to Democrat. This defection deprived the G.W. Bush administration of majorities in both Senate and House during its first 2 years. The Bush years also saw the defection of GOP Senator Arlan Specter who switched parties but did not change the balance of power in the Senate.
Most of the time these "independent" senators only show their independence when their votes don't matter. Murkowski's vote on the Kavanaugh nomination in 2018 and Collins' vote on the ACB nomination in 2020 are perfect examples of this.
It will be interesting to see how this plays out, but my original point still stands: The GOP Senate owes absolutely nothing to the dysfunctional sh!t-hole states that have been dominated by Democrats for years.
And if you think this doesn't come into play when drafting legislation and crafting strategy in the Senate, just look at what happened with the provision of the 2017 tax reform bill that capped state and local tax deductions. The six states that were screwed the most by that tax law were California, Connecticut, Illinois, Massachusetts, New Jersey and New York. If there had been even a single Republican senator among the twelve representing those states in the Senate, that provision never would have been included in the Senate version of the tax reform bill.