For me the biggest lesson for a DM is putting too much weight on a single or few dice rolls. I think everyone can agree that "Save vs Death" mechanics are terrible in play and I would say the reason those mechanics are bad is because too much is riding on that one dice roll.
I think you had an overall thoughtful post, but I wanted to single this particular section out for a reason.
Most people, myself included, often fall into the trap of assuming that everyone agrees with me- most likely because I am smart, witty, articulate, and correct. That said, there are people that for whatever reason (most likely due to defects of their upbringing, such as being dropped on the head by their Uncle Goober and/or showing an unfortunate appreciation of Bards) do not agree with me.
The actual existence, and continued popularity, of games that involve mechanics that either are, or resemble, save v. death (whether people are continuing to play "old school" editions, or clones, or whatever) would seem to belie your statement that
everyone agrees that those mechanics are terrible in play. I would even say that those mechanics are the quintessential (or, from your P.O.V., worst) example of an event that the player has no control over, that can result in death.
This doesn't mean that the player can't prepare, can't make plans, can't have contingencies, can't avoid combats, can't play safely, but sometimes, you just roll a 1.
I don't think that these mechanics
qua mechanics are good or bad necessarily, and I do think that there are sound reasons for a lot of games to move away from those types of "unfun" mechanics, but I think that you have seen credible reasons in this thread why there are those who still enjoy playing that way- sort of a rule utilitarianism; while the instant event (failed death save, character death) is
unfun, the overall experience of the game that has it, for those people, is
more fun.
So I think that people might have different reactions to your overall post; on the one hand, players might appreciate that you put in "loads of hooks and levers for my players to draw upon when things start getting desperate" to change the conditions; on the other hand, I know that if I were playing, I might feel insulted that there were these obvious hooks and levers to bail me out of a situation; it would remove my sense of agency and triumph were I to succeed because it would feel too much like
DM ex machina. That doesn't make your approach wrong- it sounds like a lot of fun! But different people have fun in different ways. Heck, did you realize that there are people that actually enjoy playing elves? Dead-eyed soulless automatons. Harumph.