I've not read the thread so I may be putting out a pile of bullet points that no one cares about and/or aren't terribly applicable. But, I'm a sucker for saying things that no one cares about and aren't applicable, so here goes!
It's so nice to know I'm not the only one!
* There is TTRPG play where the question of "who is the lead (for whatever value of lead) protagonist" is a matter for aggressive play and application of system to settle, even when (or perhaps especially when) the preplay setup might either (a) generate a character whose "protagonist momentum" (lets call it) is actually greater than others (the Master in My Life With Master is intentionally set up this way) or (b) superficially it appears that way at the outset but its ultimately settled downrange of actual play.
Disclaimer: the following all assumes group play rather than solo.
There's a difference between a) a campaign where the role of lead protagonist shifts from character to character (in the medium to long term) as the game goes along, and b) a campaign where one character is the lead protagonist all the way through.
IME few if any players have issues with the former but many - sometimes including the player of the lead protagonist! - end up having issues with the latter.
And also IME I've found any situation where there's an obvious or declared lead proatgonist (e.g. Jocasta has rounded up the party specifically to help her on her quest) to be a PITA as GM, largely because it's almost ironclad guaranteed that either bad play or bad luck is going to kill off that lead protagonist at the first opportunity, leaving everyone floundering: <
both in and out of character the players look blankly at each other> "It was Jocasta's quest, but she's dead - now what do we do?". And so, I've learned the hard way to avoid these sort of setups if-when possible.
* Personally as a GM? I'm always drawn toward/enamored with the stories of either (a) (so-called) "support characters" or (b) characters whose story tragically (and often violently) ends or just never turns out despite their best efforts. Honestly, I'm that same way with media (RIP Cormac McCarthy). Of the games I've GMed, I can absolutely point toward a host characters where the experience of witnessing their trajectory was deeply visceral and memorable to me precisely because aggressive play and application of system yielded a trajectory of distinct orientation to fulfilment (which might even include "lack of") or even decisive, defining failure.
Oh, me too. I love watching underdog characters do well or die trying, and often quietly cheer for them even though as GM I'm supposed to be neutral (and am, when it comes to laying the hurt on 'em). But I also want there to be that chance that the support (or underdog) character now can eventually become the lead character or top dog later, if everything falls in place for it; instead of being doomed to the support/underdog role forever no matter what.