I've heard that about polyester before, but in my experience it adheres extremely well. I have made full thickness deck and hatch repairs and I'm sure they will last longer than I will. I guess time will tell.
Poly can be used for repairs, but ithe interface bond is at best is about 20% weaker than a wet layup bond. Compared to epoxy that reaches 100% of its wet layup bond when applied to dry poly, and the fact that an epoxy bond is much stronger anyway, leads me to never recommend poly for anything other than initial boat building.
It is less expensive, but it comes at a price. Typically my time and labor is worth more than the increased cost of the epoxy, and I hate redoing work.