2. D&D 5e Mode = Actual 5e rules implemented. No backstab or higher ground, etc. Potions are Actions. No food during combat. True RNG. No loaded dice. Enemies have true 5e stats like accurate HP and AC. Disengage is an Action. I mean full blown D&D 5e experience. Game is harder because it is full blown rules with no cheese and nerf.
Why would you remove highground ? What would be the point of taking a good position in your system ?
Because high ground doesn't give automatic Advantage in 5e, and the mode is called "D&D 5e Mode"?
Advantage is not the only bonuses highground could give (and it shouldn't give advantage).
Highground has to matter even if it definitely shouldn't be a god mode. Delete the whole concept of verticality and positionning for the sake of "D&D 5e" is a bad idea.