Does precedent in the United States Court of Appeals for the Fifth Circuit allow defendants to circumvent FRCP 15 and FRCP 16 requirements for amending pleadings?

Question Presented Does precedent in the United State Court of Appeals for the Fifth Circuit which allows defendants to raise affirmative defenses in a motion for summary judgment or otherwise “at a pragmatically sufficient time” such that a plaintiff is “not prejudiced in its ability to respond” impermissibly allow defendants to circumvent the requirements to timely seek leave to amend their answers to assert such defenses pursuant to FRCP 15, and/or the more onerous requirements under FRCP 16 to modify a Scheduling Order to allow an untimely amendment of a responsive pleading, in conflict with Supreme Court precedent and decisions from three other circuits which hold otherwise? i