I'm not qualified to give a technical opinion but I can speak from experience. I have used TechTool Pro to defragment the drive and have not noticed any difference in performance. This is my personal experience, however, and may not apply in all situations. I have not defragged for several years and all seems to be well.

My 2¢.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365