reading your post tells me you don't understand what fine motor skills vs gross motor skills actually means. Anything that requires grasping or manipulating of an item is a FINE motor skill. Hitting, punching and kicking are gross motor skills. Further if your fine motor skills degrade so poorly under stress that using the slide release is not possible how are you ever going operate the trigger or mag release? Under some arguments for Fine vs Gross, hitting the slide release could actually be a Gross motor skill function, but that's a debate for another day.
You should probably try reading a bit more and try training with people that actually know what they are talking about before you try to become an internet expert.
I can assure you that I have more than enough experience and training on the topic to offer my opinion. If you want to nit pick, yes, you're right. Anything done with the hands is a "Fine Motor Skill" by definition. But the act of operating a small lever with a single digit, vs operating the whole slide with your whole hand is a Fine vs Gross movement when it comes to pistol handling. I certainly didn't say it wasn't possible to operate the slide stop under stress, I said the chances of making a mistake with that movement, rate higher than if you grab the slide and work the action.
Your argument of mag release and trigger operation degrading under stress actually validates my point... If you have the experience that you say you do, you'll agree with me what once someone is put under stress, their shooting and pistol handling suffers. Their groupings open up and they're reloads start to get rushed and sloppy.
I don't train for a world of targets and timers. At the end of the day all pistol manipulations should be done using techniques with the highest rate of success. In my 1000+ hours of range time, the over hand slide manipulation is what I train for and it has never failed me.
If you've trained yourself to a level where you're confident in your tactics, then that's fine. But for the average shooter, I don't think it's the right way to go.
Differing opinions make the world go round. I'm not offended by yours, and I don't expect you to get your back up over mine.