Here's the problem. Police have complete authority to control a situation where anyone POTENTIALLY involved is present, not even a suspect. Full stop. They have the ability to detain (not arrest) anyone they see fit. Now if someone resists that detainment, that has by definition escalated the situation. At that point, they have the right (whether you like it or not) to use reasonable force to control that person. And if that person continues to resist, yes, a taser is legally justified. What excessive force ALWAYS involves is using force at a level that is unnecessary to detain those individuals. That is usually overtly violent punches, kicks, baton strikes, and of course, their firearm being discharged.
What this will come down to was anything those cops did excessive in a situation where they have every right to detain someone that is uncooperative? Right now we have ZERO evidence that's actually the case, that video included. You and I may not like the optics of what we've seen thus far, but that has nothing to do with the legal thresholds involved.