I mean, to be fair, the only reason that whole "two people standing watch" thing is an issue at all is because D&D 5E only has two big levers for adjusting modifiers (Adv/Dis). In most other systems, a small +1 or additional bonus is a fine way to represent having two people standing watch, with them being around to keep each other alert and reduce the field of vision they need to monitor.
A little off track here, but we could say that darkvision ruins the Help action too.
Alba: psst. Give me a hand over here.
Brohq: Who said that?
Alba: Me, genius. Now get over here.
Brohq: Where's here?
Alba: I thought you were a "scout." Just follow my voice.
Brohq: Just because you can see in the dark . . . Alba? Alba!?
Alba:
Brohq: Great. I can't see, Alba's dead, and I'm going to be eaten by a grue.
Alba: Sorry. I saw a patrol up ahead.
Brohq: Well, that makes one of us.
Alba: Just get over here. I need you to spot for me.
Brohq: Spot!? I can't . . . see . . . in . . . the . . . dark!
Alba: Well, neither can they. So just watch over there for lights or movement. Something might pop up.
Brohq: I think I saw something.
Alba: Where? I was focused on the . . .
Brohq: Right there! ::Sticks pointing finger into Alba's point of view::
Alba: I don't . . . Oh. I see him now. Thanks for the help.
Brohq: Don't mention it. If you need me to find . . .
Alba: Shh! I need you to be quiet, because there seem to be some darkness-dwelling creatures coming toward us, and they might have better ears than you do.
I expect that to be much less interesting in a fully dark-sighted party.