And here my first multi player play through was with just 3 members. My current playthrough don't have the rogue, Gale has 14 dex, he can pick those locks.
While I get the idea, and wanting to cover all the bases, I think that's the exact reason why you shouldn't have it. DnD 5e is interestingly balanced. You can play almost any combination of classes, and still win. Larian has done a great job of adding "many ways to Rome" for most situations. Many classes can fill two roles too. Clerics are great tanks, Warlocks and Wizards can do lots of sneaky things (especially a Wizard with invisibility and high Dex)
What I think is more needed is the ability to respec the origin characters, because their stat distribution is... not god.