You make my point for me. DON'T try to rapid fire while dry firing. You were raking the slide uselessly because that's how you trained during dry fire. Don't do that."Train like ya fight, fight like ya train." when i was doing a lot of dry fire practice with snap caps only, i did a lot of draw from concealment and fired a shot, racked the slide to eject snap cap and pull the trigger again. Everytime i pulled the trigger i had to rack the slide to eject a snap cap and chamber a new round. When shooting outdoors. I (because of training/muscle memory) drew pistol, fired a shot and immediately racked slide ejecting a live round, chambering a new round and wasting time doing it. Not something i wanna do in a fight so not how i wanna always train when dry firing. I would not have thought i would have done that with live fire but...it was instilled from training that way. I have already stated that by using this device in addition to other training, my shots have gotten better and faster. Even "rapid fire shots" are better. Take recoil out of the picture for a moment. If ya have trouble working the trigger throttle control with no recoil impulse (remember, you are working a trigger pull weight that is more than weight of gun and need to not move sights off target from bad trigger press), it would be good to remedy that. I agree if i could do dry fire with a devise that simulates recoil, that would be ideal. But since i only get recoil with bullets and cant shoot everyday, i look for ways to supplement (not replace) live fire. This is one of those ways. So if i have seen progress in doing this when shooting live fire, it makes it difficult to agree with you that its useless and teaches my body wrong things when in fact it has been useful and made me better.
The negative body programming you experienced was obvious, so you fixed it. The negative body programming you get from just repeatedly pulling the trigger without having to deal with the primary limiting factor in rapid fire, recoil, is also creating negative body programming because you are very likely to try and do rapid live fire the way you have body programmed during rapid dry fire. It can't be done.
As for you improving in rapid live fire, there are two things to consider. First, accuracy over all will improve with dry fire drills. Second, I think your definition of rapid fire and mine are different. My definition is that, if I am sighting on follow up shots, I am puling the trigger as the muzzle drops back down from recoil because I have practiced rapid live fire enough so that the muzzle stops on target with no further adjustment necessary. At least that's how it happens when I'm well practiced and it is always the goal. There is simply no way to practice that skill in any way without the element of recoil. In my experience, it is also the most perishable of shooting skills. It quickly degrades unless you are constantly driving the body programming home by practicing it. There is simply no way practicing a rapid fire skill without recoil is not going to degrade that skill even more quickly.
Hell, if I'm really rusty I don't even rapid fire to start regaining the skill. I slow fire while paying very close attention to where my muzzle stops from recoil after each round is fired. I'm not doing this to get faster at getting the sight on target after it stops someplace other than on target. I'm doing it to adjust my grip positioning and tension before and during the shot so that it does stop on target after recoil. That is the key to real rapid fire.