Keep in mind that Counterspell is probably the worst, and I'm still trying to think how to implement it without constant popups if players go up against multiple spellcasters later in the game.
For the rest of the classes I worked on, honestly, there wouldn't be that much Reaction Management involved. I made notes. See for yourself if you want.
Note: It's a Google Sheets doc, so it's not exactly pretty. I hope you will look at it and get the overall idea as opposed to getting hung up on how it looks.
Also, I'm open to suggestions on how to tweak presets, etc.
I think having configurable presets would work extremely well, as long as the defined presets are well defined and correct for each spell/ability type. I see nothing wrong with this at all.
Keeps the combat and gameplay flowing while still giving players the ability to control their Reactions on their turn.
The two I still am not totally happy with are Counterspell and Temporal Shunt. They are the hardest because of just how complicated they are. However, if you have these two, and you have prompts, that would be a nightmare if you go up against a room of spellcasters. Every few seconds, "Use Counterspell? Goblin Booyahg is casting Hex."
I am still pondering them, but a default spell list seems the best way to go. You decide what spells you want to trigger them.