Why does he recommend not using a sliding patio door? That to me is about the perfect application for one?

He stated that the seal wasn't as good on the sliding patio doors over time.

I tend to agree somewhat but with a quality sliding product you have 15 years before changing it may possibly be necessary.

+1

Nothing wrong with a sliding door there. It will probably weather and wear better than a hinge door as well as fit the space better (i.e. not encroach on the footprint of the space).

So do the sliding french from a company like Marvin tend to be a better quality than a regular sliding door from the same company?

I'm not thrilled with the idea of putting in something that only has a 15 year lifespan.

The French rail is just a style of the door if that is what you are referring to.

Decent quality sliding - or folding sliding doors - will do the job and last more than 15 years. Of course you have to fit them properly for a good seal so choose an experienced fitter, a specialist fitter or buy a door that can be fitted by the manufacturer. As with anything, you get what you pay for. Untreated softwoods are likley to warp over time so treated woods, hardwoods or metal doors will perform well over a longer period.