We should be careful of our terminology. It is common to speak of someone acting "instinctively" because they can make conscious choices very quickly and competently. But, that is like saying "literally" when we really mean "figuratively." We are exaggerating (sort of misrepresenting) to make a point.
I think most fight or flight decisions are conscious choices made quickly, not reflexive decisions. It is known that when the brain is pressured or fatigued, it puts its effort into decision making, and sets aside recordation of the events. Ever drive 10 miles when you were tired and not recall doing it? Your brain made decisions, and just didn't record them in memory. Just because we may not accurately recall a series of decisions does not mean that decisions were not made, and we were only acting by reflex.
Even if I grant that some fight or flight decisions are instinctive, and therefore not the exercise of free will, that does not nullify the fact that there are fight or flight decisions which are conscious exercises of perceived free will.
Some people have never thought about what to do in a difficult situation, and when faced with a sudden existential threat, they may act in a way that appears to be without conscious thought. But others give a lot of thought to such things. For example, our military personnel spend a lot of time thinking about what they will do in urgent, difficult moral circumstances. They decide in the classroom (years before hand: "What will I do?"); they train; and then when the situation develops, they act (more likely than not) according to those decisions and training. Their actions are fight or flight, but they are performed according to well reasoned decisions made before...and since the event is slowed for them due to their training, they see more, and they perform with decisive action. This is not instinctive. So, setting aside purely instinctive decisions, our discussion here is about decisive action...deliberate actions directed by conscious thought...is that free or not? I don't think bringing up actions which are not the result of conscious thought means there is no free will. There still may be actions that are the result of free will.
Whether or not I read your next post is a decision I have made. I will. Did I freely make that choice? Or, did I have no free will, and I am compelled to read your next post because I have no choice in the matter?