The major reason your garbage crank a move doesn't work slow is because to don't have mechanical advantage over the other person.
If you can work out that mechanical advantage. Not only will you be able to do moves safely in training. But you will also be fundamentally better at fighting.
But it means you might loose more at sparring because you will screw the timing or the details and they will muscle out. And you will have to have back up plans for when they do.
So let's use the bjj arm bar as there is a lot of resource material on it.
Now if you go for the arm bar slow. They can defend it. And you can quite often get stuck there.
And you can sometimes fix that problem by reefing on the arm untill something gives.
Or you can change the mechanics of the arm bar until you can still apply it in a safe manner.
I am not kidding when I say get better.