Isn’t deadly force justified to prevent great bodily harm? I would think a taser to the face would qualify as such but I’m not a cop or lawyer so...
It doesn't matter if it is deadly force as much as it matters that it could be deadly force.
A cop does not have to wait until you're two feet away with a knife. Or take a hit to the face with a club. Or take two probes from a taser.
The courts have always allowed police to stay one step above the suspect in terms of force and this is no different.