Well, I have plenty of derp moments ...Not sure how many times I'm going to have to state this.
The issue is that they're two separate reactions that accomplishes two different things. The hand seal is specifically used for kneading chakra while the outflow of chakra in order to even use Hiraishin is a separate reaction. Regardless of whether or not the hand seal was formed, Sasuke still kneaded chakra and released it for Susano'o while Minato failed to even release chakra for Hiraishin.That is what happened. Sasuke didn't react faster than Minato could react as Minato is blatantly shown reacting. Sasuke put up Susanoo faster than Hiraishin could activate but as for reaction speed Minato is shown reacting with a hand sign before Susanoo was put up.
Who said Sasuke has inferior reaction speed to KCM Minato based on anything said in this discussion in the first place? Even if I did, how does Sasuke noticing Obito change anything that I've said here?
Evasive speed is reaction speed and regular movement speed, and you can get an idea of their striking speed in relation to each other by seeing them match each other when they saved Sakura, but again, there isn't going to be any real difference. Sasuke would strike faster if he has a sword though.
Well, Naruto and Sasuke didn't attack simultaneously because of having equivalent speed, they attacked simultaneously because they were utilizing a combination through Enton + FRS. I think this is a tricky subject because I believe SM Naruto is more reflexive than KCM Naruto, so referring to how EMS Sasuke battled SM Madara is the simplest route to argue Sasuke's superior speed, but you don't believe that, so there's not much I can say.