It’s extremely simple: don’t assault people.
We know to a certainty that TM assaulted GZ and not the other way around. There is not a mark on TM except for the gunshot wound. GZ’s mashed nose and cuts and scrapes on his head certainly did not happen after the shooting. If you assault people they will defend themselves.
Florida law is very clear, a person is justified in using deadly force if he or she reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or herself or another or to prevent the imminent commission of a forcible felony Fla. Stat. § 776.012(1)
Having your head beat against concrete can cause death or great bodily harm and it is reasonable to believe so when it is your head being beaten.
http://www.leg.state.fl.us/Statutes/index.cfm?App_mode=Display_Index&Title_Request=XLVI#TitleXLVI
Agree with all points of your post.