i feel like I'm missing something. You're basically saying they need to just redo their entire combat and make it like Solasta. that's NOT going to happen. If they were to implement player controlled reactions TO THIS GAME CURRENTLY, it would be SLOWER than it is right now. Of course if they completely changed the entire system so that reactions were seamlessly integrated into the entire system, it could possibly be as fast as it is now, but then it would be a completely different system.
Well yes and no.
Surely it depends on the outcome of the reaction? If I take less damage as a result, then I do not need to drink a potion on my turn and can concentrate on damage, thus speeding up the encounter (or in this instance regaining that lost time). Plus I prefer for me to be interacting in the combat vs waiting my turn. I am not fussed on combat taking as long as it needs to, as long as I am INVOLVED.