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.
Only slowed down by a keyboard input though. That's still faster than a QTE and the reward for giving the player input outweighs any slowdown from a keystroke.
