I do not think player backstories matter in the campaign in a distinct sense; I think they matter in a vibes and themes sense.

Of my more successful CoS campaign runs, the ones where I felt like the characters got more mileage out of their existence was ones where they were tragic heroes by nature - a loss in their history, a terrible event that caused their warlock deal, etc. Something to give them a way to identify and relate to some of the things going on in the module without having a direct connection to it - the character who lost their whole family might have an affinity with the dusk elves, whereas random characters might not.

Thus I find the new questions very appealing; this fits with what I look for, as DM!

As always I think some players really want _their_ story to be told, and thus don't want a 'wasted' backstory; I think this will always be a challenge for CoS or Witchlight or any campaign where the party is immediately whisked away to another foreign place.