Hiya!
Since when was "+2
or Advantage" a thing?

I never read it that way. I always read it as "when there's a lot of little good or bad things and you don't want to keep counting, just stop and say Advantage or Disadvantage". I also read it as "when there's one or two little good or bad things, just apply that bonus/penalty". I also, also, read it as "when all of the above applies, use a both".
The key thing I "read" into that rule is this:
"Here's a mechanic to make your game run faster".
If you get to a point where trying to total up numbers is slowing things down...drop it and use the Adv/Dis mechanic. I never saw that as being mutually exclusive to any other bonuses. I use both, but cap at +/-5. Once I get either above or below 5 for adjustments, I usually just jump to the Adv/Dis mechanic.
I also tend to apply my 'numbers' to AC or DC...not to "rolls".
For example: An archer standing in tall vegetation (at about eye-level) shooting at a well-hidden tasloi up in a tree with the sun behind it. I look at the tasloi's AC, say, 14. Then I look the factors; I'd give +2 for cover, +1 for archer being in tall vegetation, another +2 for the sun being behind the tasloi through the trees. That's +5 to the tasloi's AC...so it's AC 19. Does the archer have anything giving him Adv/Dis? No? Then just roll. Or, yes he does? Maybe he is Exhausted? Ok, roll at Disadvantage. The tasloi's AC is still 19. I didn't just leave it at 14, then start applying 'negative modifiers' to the archer, eventually ending in..."Oh, er, well you're already Exhausted, and you can't stack/add Disadvantages, so roll at Disadvantage against AC14".
I guess what I'm saying is... either I'm doing it wrong (which is fine; I'll keep doing it wrong because it works for me), or all of you are (which is also fine).
^_^
Paul L. Ming