It wouldn't be me if I didn't respond...Both gel and automotive paint will flex. I use Billy B as a fine example...arguably the best out there...he uses all solvent based automotive urethane paint. It holds up very well. Now keep in mind that Billy's discriminate clientele take exceptional care of his end product. Gel coat is a finicky product...not the product itself...but application process. I have seen the best and I have seen the worst. Here lies the problem with gel coat. Color hold out and product applied to thick. Both issues need to be looked at. Gel applied to thick WILL crack..period..no ifs and's or but's. And I've seen some of the best out there deliver a product that does not produce color hold out over a long period of time.
Here's, to me...the best of both worlds..now this is a highly held secret I believe. I have used water based color under clear gel coat...OH NO MR BILL...I can hear you now..So let me explain if you wish to read more..Duratec makes a gel product called Sunshield Clear. It's clear like water clear. Beautiful product. PROBLEM...it sands like concrete and buffs even harder...but in the end it's the best I've seen at gloss and color hold out. So the advantage is this. Tough product the will take bumps and bruises...but you can use a beautiful color under it. Best of both worlds. Just be prepared to work like a slave to get your shine flat and shiny.