I edited my previous reply to your post to point out that your proposal would often increase miss chance by 15% instead of decreasing it.
Also I explicitly stated what would be acceptable hit probabilities for me. At a minimum 85%, more reasonable 90% ( that average includes both cases when you have and not have advantage/disadvantage ).
And I do not know where you see inconsistency in my post. On the other hand, it looks like you do not consider misses as an issue now in BG3, while your own compilation post mentioned it.
No it wouldn't decrease your %to hit because D&D has MANY opportunities to grant advantages.
Here is a list made by another member of this community.
The Gameplay: - Here is a non-exhaustive list of class features and spells that grant Adv or impose Dis for characters between levels 1-4:
General Actions:
1. Dodge/Help
2. Dropping Prone against Ranged Attacks
Spells:
3. True Strike
4. Vicious Mockery
5. Cause Fear
6. Command (certain instructions)
7. Compelled Duel
8. Ensnaring Strike
9. Entangle
10. Faerie Fire
11. Find Familiar (Help Action)
12. Fog Cloud (Depending on types of sight)
13. Grease
14. Guiding Bolt
15. Protection from Evil/Good (Against certain enemy types)
16. Sleep
17. Snare
18. Tasha's Hideous Laughter
19. Zephyr Strike
20. Blindness/Deafness
21. Blur
22. Darkness (Depending on types of sight)
23. Heat Metal
24. Hold Person
25. Invisibility
26. Maximilian's Earthen Grasp
27. Shadow Blade (Depending on lighting)
28. Web
Class Features:
29. Barbarian - Reckless Attack
30. Barbarian - Wolf Totem
31. Barbarian - Ancestral Protectors
32. Bard - Words of Terror
33. Cleric - Warding Flare
34. Cleric - Invoke Duplicity
35. Druid - Multiple Wildshape forms that grants Pack Tactics (Wolf, etc)
36. Fighter - Distracting Strike
37. Fighter - Feinting Attack
38. Fighter - Goading Attack
39. Fighter - Menacing Attack
40. Fighter - Trip Attack
41. Fighter - Fighting Spirit
42. Monk - Patient Defense
43. Monk - Open Hand Technique (knocked Prone)
44. Paladin - Conquering Presence
45. Paladin - Nature's Wrath
46. Paladin - Abjure Enemy
47. Paladin - Vow of Emnity
48. Paladin - Dreadful Aspect
49. Ranger - Umbral Sight
50. Rogue - Assassinate
51. Rogue - Master of Tactics
52. Rogue - Cunning Action (Stealth)
53. Sorcerer - Eyes of the Dark
54. Sorcerer - Tides of Chaos
55. Warlock - Hexblade's Curse
56. Warlock - Pact of the Chain (Help from Familiar)
This list you can add an advantage when your ennemy is surprised or the optionnal flanking rules (if 2 allies are in melee against a creature = both have advantage against this creature).
You would be able to add those two bonuses instead of only having an easy and cheap advantages... Leading to more tactical thinking and synergies which is I guess, what you asked in all your thread.
Only those that don't want to think about how to have an advantages would have a lower %to hit, and those who don't want to think in a tactical turn based game usually choose an easier level of difficulty... Leading to the same or an increased %to hit depending what parameters larian choose to tweak.
Your suggestion completely change how damages roll works, so yes it changes the basics and the balance of the system.
At the moment playing without highground or backstab advantage doesn't work at all.
Not sure you notice it, but the difficulty is completely broken at the moment.