**Abbreviated the quote** The big picture points I agree with and I wanted to highlight the points that supplement my thoughts on how height advantage impacts gameplay. My post will be focused primarily on height advantage (higher ground). There are definitely other mechanics worth talking about, but I want to stay on-topic for this thread. Also I feel height advantage is a higher priority to address than backstab.
Originally Posted by Isaac Springsong
Summary: In the 5e ruleset, Advantage/Disadvantage is the most powerful impact on gameplay... Because it is so powerful, all sources of Adv/Dis in 5e come at either a cost of resources or a potentially penalty to the user, to balance out the sheer power of the mechanic. Currently, BG 3 subverts this balance by providing always available sources of Adv/Dis in the form of Height and Backstab, both of which require nothing more than having your character in the correct location on the map... This makes the 5e sources of Adv/Dis nearly useless as they are all more costly or penalizing...
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.
There are a few class abilities that can add a higher static modifier (such as a War Cleric's Channel Divinity that can add +10 to one single attack roll) but those are rare and always limited in amount. It is a large reason why 5e is generally much more balanced that prior editions of D&D with far less ways to truly 'break' the game.
Over the course of 17 'levels' of CR, the enemies AC only increases by an average of +6. Just having Advantage almost cancels that growth out entirely.
If you take a level 1 character and a level 17+ character, give them the same stats and the same weapon, the total difference in their to-hit roll will be +4. A level 1 character has a proficiency bonus of +2 and a level 17+ character has one of +6. The difference between these otherwise the same characters is less than the difference from Adv/Dis. That is how strong Adv/Dis is mathematically.
You can see why getting Adv/Dis is such a huge deal in 5e rules, and why being able to have them should be considered such a huge impact on the mathematics at play.
Possible Solutions: First, remove granting Advantage/Disadvantage for Height and Backstab... there are enough ways to get Adv/Dis, BUT they are all balanced by having a cost/penalty associated with using them.
...if Larian still wants to incorporate having a benefit for having higher elevation than a target and/or maneuvering near a target, please incorporate the Cover and Flanking mechanics as described in the first linked Primary Topics Link. Cover provides a potential benefit for being higher than your target because your target will not have Cover from your attack. Additionally, you will possibly have some Cover from attacks from below due to the surface providing elevation. Flanking also requires at least 2 allies in melee combat, increasing the risk to those characters for the reward of potentially having a greater chance to hit.
Alternatively, if Cover/Flanking is deemed to difficult or impossible due to the limitations of the DoS engine being used, then replace Adv/Dis with a flat +2/-2 bonus (which is the bonus provided from Cover and Flanking respectively). This makes players still want to seek out sources of Adv/Dis due to their higher mathematical benefit, while also not invaliding all of the listed spells, actions, and class features.
I was going to write up a thread about how advantage from a greater height and disadvantage from enemy attacks is too much benefit for moving a character a few units up in 3D space. Thank you Isaac for making this thread.
More on Why High Ground Advantage/Disadvantage is Problematic for BG3
Isaac wrote a lot of good points that highlight how problematic height advantage is in keeping combat engaging. By combat engagement I'm referring to the player's perspective of having meaningful choices to make. In the current patch, it's frequently just going for high ground in most of the fights. The current state of the game makes me consider reloading a save if I entered combat from a bad angle and I can now see an angle that would give me free advantage at the start of combat. That's not something a player should be considering, but after tens of hours in the game those are frequently my first thoughts.
Height advantage provides too many benefits how easy it is to obtain. I want to propose removing disadvantage on attacks from lower ground because high ground is just too valuable in the current game meta. It just doesn't make sense that a character standing on top of a hill, outside of cover, is harder to hit. Baldur's Gate 3 also has collision checks for projectiles, higher ground currently gives a lot of defensive value too.
My Thoughts on Possible Solutions
1) I'm all for trying out Isaac's proposal for a +2/-2 bonus for higher ground in early access. I like the idea of higher ground having benefits in the game and this change would be a step towards correcting how over-tuned height advantage is. And give the player more meaningful choices than the current state of the game.
2) It's also worth considering having height advantage only give a +2 to attack rolls. If a character is standing out in the open there really isn't a reason why they would be harder to hit and Baldur's Gate 3 already has collision checks for if projectiles could hit. Anything the character could cover behind is already possibly protecting them, so disadvantage on attacks from lower ground is greatly exacerbating how impactful high ground can be in Baldur's Gate 3.
3) Flanking is a "nice to have", I can totally understand why it'd be hard to implement as 3D space becomes congested. There is the possibility of a domino effect with flanking where immediately after your character flanks an enemy you can be flanked by another enemy. I think it would be fun to experiment with variant-flanking (tailored for the video game experience) to give more value to terrain that is not higher ground. But that could congest the combat AI and slow combat down.
4) Cover is another "nice to have", I think it would be cool to add a cover mechanic. However, I can also see how it'd be a lot of work for the developer to take the time making objects capable of providing cover, and testing that the mechanic works as designed.