Again, little of that matters. Your taser example would be considered an accident. Here, an extremely charitable jury might give negligence, a just one would probably give depraved heart. As for the training, some of it is common sense. A reasonable person knows that the neck is fragile, even without training.
But we know he didn't break the neck, and if the early autopsy data is to be believed, didn't strangle him either. The court is supposed to sentence him for things he has done, not for things he *might* have possibly done but didn't happen.
He had a pretty screwed up hold, but that's procedure, training and competence issue.
As far as i understand the part that contributed to Floyd's death is position and weight applied, and it would still apply even if the hold was performed perfectly.
The disregard for the unresponsiveness following the disregard for the "I can't breathe" claims is what is chilling though. for three minutes, he put his knee into a man's neck who was out cold.
And that's where procedure and the question of first aid training comes in. After all, he had no access to life sign data, and going limp would simply mean no more resistance.
3 minutes is long, but not unthinkable for them to notice something unusual, especially if their first aid training is as sloppy as their holds.
As i said "i can't breathe" claims during arrests are "tuesday" for any experienced cop, so i would not put so much attention to that. For example, half the funny videos about odd arrests or stupid people getting themselves arrested include some variation of that, and very often it is ignored.
It looks very bad for people who have no idea about what they are looking at, doubly so if they are looking for reasons to be outraged, but optics from perspective of the clueless and biased are not what justice is supposed to be based on.