Admittedly, Z is not an LEO, so the continuum of force model does not apply in totality...
All that is necessary for Zimmerman to have acted in a justifiable way is: Did the other party initiate the actual fight, and did Zimmerman reasonably fear that he was at risk of death or serious injury?
That's it.
Based on the evidence presented, I would say the answer to both questions appears to be yes.
The answer to the first question is not absolutely, 100% certain. It is PLAUSIBLE, though not at all likely, that Zimmerman COULD have thrown the first punch.
That would undermine the claim of self-defense.
But there is absolutely no hard evidence in favor of that, and there is CERTAINLY more than a reasonable doubt against it.
The answer to the second question appears to be an indisputable YES.
I see no sane way to return any verdict other than acquital. At this point the case appears to be so weak that it should NEVER have come to a trial.
Insofar as the trial goes, I would tend to agree.
However, in the larger scheme as I mentioned a SYG continuum of force model would be of use in society at large, not just limited to the trial itself. For example, public understanding and acceptance of a SYG continuum of force model would tend to help avoid currently anticipated street riots if charges are dismissed or a not guilty verdict is returned.