All very valid questions! And all questions that are being thoroughly
hashed out in 5e-centric spaces among people who
both object to the blatant use of GM force and railroading
and also genuinely want to play the 5e adventure paths. Or people who have been genuinely influenced by games like
Dungeon World and want to bring some of those principles to bear even when running 5e adventure paths. Or people who watch critical role and are "using" dnd as the base to create more open
experiences. Or, OSR spaces where people are
rethinking the role of what you call backstory and how it is developed. (Or people in those spaces
going further and
mixing their
experiences with games like blades in the dark and
rules-lite OSR.)
One reaction to your questions is to give up on "trad" games and play story-now games. But there's lots of interesting cross-pollination and experimentation going on that I think is worth paying attention to, personally.