Agree with OP. Especially the height mechanic gets tired very quickly in my opinion. In the first encounter past the tutorial against the intellect devourers, the moderately sloped ground can make a night/day difference depending on which direction you are attacking from.
Concerning the argument that it feels bad to miss frequently: it also feels bad to consistently get hit by the enemy unless taking part in this race-to-the-top mini game.
Apart from the various skills that directly compete as ways to grant/inflict advantage/disadvantage I would also draw a comparison to other conditions. Targeting a creature in darkness (without dark vision) or heavy fog causes disadvantage. Aiming upwards at a moderate angle is way easier than that. Using a weapon a character is not proficient in removes the proficiency bonus, which is +2/+3 in early levels. Aiming upwards should be easier than using a weapon the character does not know how to handle.
I agree that effects of movement should be more pronounced in a video game compared to TT and height can play a part in that. But I think significantly smaller incentives can accomplish this goal. E.g. a range modifier for ballistic weapons would by itself encourage seeking high ground. And perhaps an attack bonus of 1 with the possibility to increase it through abilities in some classes. IMHO this would already be enough to seek out as an advantage without devaluing other choices too much.
Originally Posted by lx07
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 scenario you are referring to exactly. Assuming the base scenario is having to roll 3+ (90%), rolling that with advantage would be 99%. Giving a bonus of 2 (rolling 1+) would produce 95% when respecting critical failures. And even ignoring critical failures (100%), the increased chance of critical hits typically makes up for the 1% lower probability.