Well, the model you say exists obviously is not sufficient to support SYG in practice, would you not agree? That is, it is insufficient if people like Z who use SYG can still be prosecuted in spite of common sense.
Those same political concerns would also have outweighed any OTHER, more complicated model that you could possibly propose.
Whether or not Z is found guilty, one of the larger issues is a chilling effect that the mere prosecution of Z implies that many people will be more reluctant to count on society's law to support their well being when using SYG. Ultimately this results in more disrespect for the law. I would welcome what you regard as a more complicated model over anarchy or the loss of innocent life due the the chilling effect that the prosecution of Z currently has among law abiding, CW carrying citizens.
Saying stuff over and over again like Z is innocent on FR is like preaching to the converted. OK, ...but so what? This is an open discussion and IMHO we can and should be open to larger implications and discuss larger issues raised. Think small, stay small.
Zimmerman didn’t use stand your ground. He had no place he could retreat to.