Your conjecture that GZ "did not have to fight Trayvon" is not found in evidence, neither is "he just pulled out his gun and ended his life". Court testimony estimated the fight went on for 40 seconds before the shot was .
Yes it is. The fact he ignored advice/instruction/suggestion/hints/allusions/winks that he should not go after the man he said was acting suspiciously is evidence that he did not have to fight him. He could have stayed where he was and let the police do what they are empowered and trained to do, and there would have been no need to fight.