Convoluted? lol. That's hilarious. How is this convoluted?:I
Bruh. How is it not convoluted? Enemy Current HP > X. First of all, it's not even clear if we'll have the enemy hp visible to us at all difficulty levels. Secondly, it depends on the enemy. If a dragon has 15 hp remaining, I'd spent my spell slot for Smite, if it's a goblin with those same 15 hp, I would not. It has to be a VERY complicated and convoluted if-else system to be at least somehow close to what actual reactions can provide. Or let's take Counterspell. You expect a new player (or any player for that matter) to go through 400+ spells to tune the reaction? And what if in some cases I would want to counter Shield and not in others? Reload the combat and tune the preaction beforehand? Nah.
To be fair, such an implementation wouldn't *have* to be that complicated. The criteria for Smite could solely be based on HP, and not care about enemy type or CR or anything else. There's some middle ground balance where the combination of "ease of use/simplicity" and "control over reactions" is highest.
For Counterspell, you don't get that until level 5 so a player will already be a bit familiar with the spells in game, and you also essentially will only have to care about levels 1-4 spells at that time, not ALL spells in the game. If the default Counterspell options activated on all level 2+ spells and no spells below level 2, then a person could go on a case by case basis throughout the game. "Oh, I counterspelled that? Hmmm that doesn't seem worth it; let me turn that 1 specific spell off." or "Oh, wow that's [Bless] a power 1st level spell; let me add that to my Counterspell list."
I still think it is too complicated for this type of game and doesn't provide enough control, but it doesn't need to be extreme "you can tune every possible condition you can think of" to be more functional than the current BG3 reaction system. (I prefer prompts > overhauled reactions appropriate for lack of prompts > preset reaction tactics).