Originally Posted by Isaac Springsong

The Maths: - In 5e, in general, having Advantage is roughly equivalent of having +5 to your roll. Disadvantage is roughly equal to having -5 to your roll. This means if one character is rolling with Advantage, and the other character is rolling with Disadvantage, then there is the rough equivalent of +-10 between their rolls. Additionally, Advantage doubles the chance of rolling a critical hit, and makes critical failures much less likely (5% normally vs 0.25% with Advantage), vice versa for Disadvantage

Originally Posted by Isaac Springsong

Looking at the graphs in the link it seems is only +/- 5 at 10; at 19 it is +/- 1 (linked article says average is +/- 3.325).

Wouldn't this mean if you had a high (say 90%) unmodified chance to hit, using a flat +/-2 would make it more likely to hit than using advantage?

Not sure what proportion of attacks are long odds rather than midrange (where advantage is higher) though or if it matters. I can't work it out in my mind...