Solution* that addresses both your issue and the prevalence of advantage in 5e via backstab & high ground: Full Darkness should grant disadvantage to all creatures (unless they have superior darkvision or Devil's Sight), but Dim Light only grants disadvantage to creatures without darkvision.
-->There is still a difference between races with and without darkvision, but it is lessened (only relevant in Dim Light)
-->It is super easy to get advantage (via backstab & height), which will cancel out with the disadvantage from Full Darkness to normal attack rolls!
Finally, Larian adjusts** it so that advantages don't totally cancel out: X Advantages + Y Disadvantages result in Advantage if X>Y, Disadvantage if X<Y, and normal if X=Y.
-->This will encourage players to use (dis)Advantage-granting spells like True Strike, Blur, Faerie Fire, and actions like Shove Prone (if implemented) in addition to high ground & backstabbing.
*I don't think BG3 has dim light(?), so Larian would have to implement a better lighting system for this. But, given that they already can distinguish between lit and "obscured by shadows", this should be a relatively simple fix? Just adjust what "distance from light source" results in fully lit, dimly lit, or obscured by shadows.
**I feel like this may already be true in BG3; does anyone know? I would check but I've uninstalled the game...