About 3/5 of playing a rogue is asking the DM, "OK, but can I get advantage if I do THIS?" (the fighter equivalent being "OK, but can I have more damage dice if I hit him with THIS?") and then hoping that your stunt is entertaining enough that the DM allows it. Every good DM, or rather I should say every DM who is slightly subpar or better, knows that there should be environmental hazards and opportunities for the players. These are by far the most ubiquitous sources of advantage/disadvantage in any DnD game, but they are either impossible or extremely difficult in a video game. This is what high ground advantage represents. If you wanted to make it more PnP-like, just require a perception check before the attack to determine if it gets advantage.
Honestly in the majority of fights I would say the impact is overstated. Either you need melee guys keeping the enemies on the ground, or the enemies will simply seek the same level as the party. If you have melee guys involved, then 1-2 members of your party are NOT making ranged attacks from above, in which case all of those other spells and abilities that detractors claim are now useless still have significant value. If devoting your entire party to ranged attackers who always seek the high ground is truly so powerful, and all other builds so weak, that the player is effectively "forced" to design their party that way, as one commenter claims, I have not observed that. While my archers are useful, contributing members of the party, my first playthrough used a druid and a fighter to pretty good effect. I have not noticed that my current playthrough using an archer ranger has been significantly easier, even though he does get advantage from high ground as often as possible. (But not always, and he is 100% reliant on other party members or his animal companion to keep enemies away from him, as even with Jump enemies can reach most perches that players can.)
It does appear that the game is simply adding +25 for each source of advantage and -25 for each source of disadvantage, instead of actually rolling two numbers. This is ought to be changed immediately. My character with two sources of advantage and one source of disadvantage should have the same chance to hit as a character with two sources of advantage, but the game reports one's chance to hit as 55% and the other as 80%.