I think the egregiousness comes not from the move itself, but the duration a excessive use given the person was already subdued, in hand cuffs, on the ground, and not resisting.
I don't think anyone would complain about a knee on the neck of someone actively resisting arrest while they were getting the situation under control.
Alternatively another technique locks the neck between the foot and the knee and again you aren’t supposed to put your weight on the neck unless you want to kill the person.
Untrained cop on a power trip using improper technique to subdue a person for a fucking forever and a half is a recipe for disaster.
BTW I would bet on most cops not knowing how to perform this properly the only reason you usually don’t have casualties and fatalities is due to the fact that they only hold the suspect in submission for a few seconds until they are cuffed or until their partner arrives to hold them down not like 10 min or what ever that it was.
What makes you assume the cop wasn't deliberately trying to murder? Or did you mean it more as an 'in general' statement?