I'd be absolutely fine with the just one roll rule. Not a big deal. Point buy is boring though it's become the standard largely in dnd crpgs even though it's not the standard in the 5e PHB. LOL But, rpg devs are known to be lazy abd too keen on 'balanced' because some players ate loud and think that dnd is a competitive sport.

And, as I already pointed out there's already an easy fix fir MP. Let the host decide just as they'll likely get to decide difficulty abd other basic 'rules' for that campaign. Problem sold.

Unlikely but this is what I'd do if I were Larian:

1. Roll 3d6 x6 (option of setting it in order, and have an 'extra roll")

2. Roll 4d6 x6

3. Low PB

4. Medium PB

5. High PB.

Choose at start if campaign. Host in MP sets the standard for the campaign they host. Much like they decide difficulty, abd other optional stuff.

EVERYONE WINS.