This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.
No, it is not a discovery request. The Complaint and Answer and Affirmative Defenses frame the issues to be tried. Florida Rule of Civil Procedure 1.100(a) states that "if an answer ... contains an affirmative defense and the opposing party seeks to avoid it, the opposing party shall file a reply containing the avoidance." This is just the Plaintiff's way of saying he does not agree that your affirmative defenses are issues that should be tried.
the demand strict proof thing is just stilted lawyer talk. it doesn't force any extra burden on you because you already have a duty to prove up your affirmative defenses throughout the case and at trial.
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