Whatever you decide, I'm sure plenty of people will be curious to hear how it shakes out so keep us posted!
Reactions/AoO’s and readied actions all seem to contribute to interrupting the flow of a round. This interruption is creating confusion about who’s turn is next. This sometimes means people miss a turn even when paying attention. I haven’t liked AoO’s since third edition because they are cumbersome and insipid. I feel like countering spells is a worthwhile endeavor. How would you handle countering?
For what you are wanting to do simply make counterspell a bonus action they use on their turn that counters the next spell cast. If no spell is cast by the time their next turn occurs then they recover their slot. You could also give them the option of using it when a spell of their choice is cast.
That said, what you are proposing is a terrible idea based on rather faulty reasoning.
For most classes in 5e for most of the game an AoO is 50% to 100% of the damage they inflict on their turn. I almost feel like you are basing your bad opinion of AoO's solely on a level 20 fighter.
Also keep in mind the DM is nearly completely in control of how often AoO's come up in actual play.
I guess you meant negative opinion.
I have never seen a level 20 fighter. I did just finish a high level campaign with level 20 characters. I have this opinion because actions “off turn” throw my table into a shambles.
50-100% of the damage they do!? Now that must be hyperbole or players roleplaying pacifists.
I realize that I may be seeing a problem that my table does not. I would be lying if I said I wasn’t looking to see them play in hard mode. I am going to talk to all of my players and see if they are interested.
I like amped up difficulty for myself but I understand that it’s not for everybody.
You are the DM, you have infinite dragons. You don't have to take things away from players to make a difficult game.
Yes 50% to 100% of the damage a player inflicts on their turn will be inflicted by an AoO on turns they take AoO's. Level 5 fighter. 2d6+4 + 2d6+4. AoO = 2d6+4 = 50%.
I do have infinite dragons. I would rather not have to reach into that bag or do the accounting.
Then why do you want to reach into this bag and do this accounting? Especially considering the changes you are proposing aren't going to significantly increase the difficulty of the game.