I don't think that you can exercise such fine motor skills while you are shooting up a school or other mass gatherings - which was the whole point of the ban in the first place.
I don't understand the kind of sociopathy required (by the judges in question) to seek an excuse to pedantically redefine a device whose whole original purpose is killing people en-masse.
I'm not interested in discussing the first paragraph but for the second; as I understand it you have to define something before you can regulate it. The pedantry is over the definition of a machine gun in that a bump stock doesn't really apply because each bump is a separate action by the operator, and the court apparently agreed. The definition of a machine gun can be changed perhaps to define a maximum rate of fire instead of number of rounds fired per trigger pull or something.