I think that just like serious snow gear makes for the best outerwear in winter / snow, serious sailing gear makes for the best outerwear when you're going to be outside in the rain for a long period of time.
A lot of the more commercial "waterproof" outerwear products are made of polyester fabrics and then treated with something like Teflon to make them waterproof. Note the comment from
@Scarlet16E that his waterproof shell from REI lost its integrity - that's what happens.
The offshore outerwear from HH an Musto are made from several layers of waterproof fabric with breathable layers in between so you're not sweating your balls off as if you were just stuffed into a plastic bag. Plus, they're specifically cut to allow movement so you don't feel constrained. And Helley Hansen, in particular, has perfectly good insulated jackets that you can get on sale for a couple hundred bucks. The Musto stuff is almost always going to run you a minimum of $500 per piece, the occasional clearance sale notwithstanding.