This is a common misconception, though, about the preset suggestion for Reactions. For 99% of all Reactions, it is NOT hyper-organizing.
Reactions (Default preset is the first option listed)
Shadowheart Reactions Attack of Opportunity - All Enemies / Selected Enemies / Off
Lae'zel Reactions Attack of Opportunity - All Enemies / Selected Enemies / Off
Astarion Reactions Attack of Opportunity - All Enemies / Selected Enemies / Off Uncanny Dodge - All Enemies / Damage > 10 / Off
Wyll Reactions Attack of Opportunity - All Enemies / Selected Enemies / Off Hellish Rebuke - Off / All Enemies / Selected Enemies
Gale Reactions Attack of Opportunity - All Enemies / Selected Enemies / Off
Spellcasters including Gale, Arcane Tricksters, Eldritch Knights, etc. could then have the following reactions as well IF they choose them and IF they prepare them:
Shield - All Enemies / Magic Missile Only / Melee/Ranged Only / Off
Absorb Elements - All Elemental Types / Selected Elemental Types (Acid, Cold, Fire, Lightning, Thunder) / Off
Counterspell - Default Spell List / Custom Spell List / Selected Enemies / Off
To be clear, would these reactions would happen automatically in your suggested system, on the first valid enemy (either of "All Enemies" or enemies that you "Select" Each(?) Turn) that triggers it?
Or does the game show y/n prompts, but only activates for your chosen presets?
At first, it was just auto, but I thought a separate toggle could control prompts if people like prompts. Those who like prompts toggle them on.