unless you have NO control over the reaction, the combat is going to be slowed down by a player controlled reaction system. Go ahead and show me how a 2 minute long fight would be shortened by adding in more player input. Adding in more input by the user is going to add time to combat, so unless you're removing something that is already in the game, it's going to be slower.
Sure thing, here you go: This thread
Here addresses your concerns. It contains several video links that show a near-5e combat system which involves a responsive reaction and player decision point system as part of its base mechanics. The videos show several things, the most stand out of which are that the ability to use and control reactions in a player-directed way heightens interactivity, and speeds up the overall pace and progression of combat compared to how those fights would run without that system in place, and leaving players to sit entirely passively through enemy turns without being able to react or curtail them flexibly. It also shows quite clearly that the use of the reaction system doesn't add to combat time in any noticeable way, and that compared to longer delays, such as those taken by an already quick-deciding player to decide upon their moves each turn, the use of reactions was insignificantly small in terms of time consumption. Have a look at the thread, have a look at the videos, and if your opinion remains the same, I'd welcome you to explain how and why, with respect to what's been shown.
Pretty sure we just had this talk in a previous thread
Yes, we did, and you had no legitimate response there either, and did not acknowledge the demonstrations and proofs that were shown, and simply reiterated your stance without evidence or back up in the face of actual demonstrations that showed the falsehood of your assertion. Please actually acknowledge the proofs offered and give your equally well demonstrated counter to them, beyond blind assertion to the contrary, which you still, despite several iterations of this discussion, have never done. The demonstrations provided actively prove the opposite of what you're saying, and your only response is just to assert your stance again in the face of them. You never respond to the actual arguments or demonstrations made; the thread is still there waiting for you to do that. All you're doing by continuing to assert this every time it comes up is spreading wilful misinformation. Please don't.