We’ve done a lot of cat rescue over the years, so I’ve picked up a fair amount of useful information. When cats are babies, their light weight allows Mom Cat to pick them up by the neck and move them around. This pinches the nerves in the neck, paralyzing them, which is very convenient for Mom. When they are adults, the same “scruff” neck pinch, used by a human, will paralyze the cat, but because of their much greater weight as an adult, if you pick them up by the neck it can cause damage to those nerves. If you need to move Crazy Cat around (and I’ve needed to! LOL!) then scruff them first and (as gently as possible) pin them down. Then keep them scruffed with one hand and pick them up with your other hand, supporting the weight. That way they’re immobilized (okay, mostly) but it doesn’t hurt them.
As for scruffing as a discipline tool, it works great. I haven’t had to do it in a long time, but if a cat really gets out of line I scruff it, bend down and get close, and sternly (not loudly) just say, “No. No. Not okay.” They really hate this, because they’re essentially reduced to being a kitten, with you as Stern Mom Cat. Then separate it from the other combatant and let everyone chill. If you use the same short verbal phrase every time, eventually you can just use the phrase and they know a scruffing is about to occur. They will usually stop the behavior then.
Everything I know about raising kids, I learned from my cats . . . LOL!
That discipline method sounds about right to me! Loud voices don’t work with a cat; all you do is scare it away. With my cats, all I’ve ever had to do is make eye contact and say firmly, “NO.” I might get a little feline backtalk, and I might have to repeat the “no” a couple of times, but 99% of the time it works.