You might want to take a long look at materials and longevity. Diving suits tend to come in three types, none of them GoreTex.(G)
The least expensive are calendared nylon, i.e. cordura cloth with a waterproof plastic layer hot-rolled onto one side, sometimes with a third protective layer over that. In five or ten years, used or not, the waterproof layer delaminates and you start leaking. Not what you want for a survival suit.
Then there's "neoprene" aka "foamed neoprene" like a typical wetsuit. With glued and stitched seams, it is much more durable. Except, if the neoprene has been foamed with chemicals, it tends to contract and shrink as it ages. In five years a Large can become a Medium. The better stuff is nitrogen-blown, the bubbles are formed by expanding nitrogen gas as the neoprene cures, and that stuff is stable. And about twice the price.
And then there's "crushed neoprene", just as durable but less buoyant, which is not something you'd want in a float suit. Or plain solid rubber, like Viking brand dry suits, also not something you'd want (no insulation, great durability, easy repairs) in a float suit.
For a gumbie suit? Nothing will compare to a good nitrogen-blown neoprene suit. The materials simply are all different, horses for courses. For a kayaker, GoreTex is great. For a diver, worse than useless.
I'd suggest there's really very little to compare, aside from brand quality choices, of the appropriate material.
1. Yup, GoreTex has lifetime durability limits, thought they have come far from the early products. I have not had 3-layer GoreTex fall apart in well over a decade, so I'm not sure whether that concern is still valid. I would also counter by stating that used on a regular basis sailing and kayaking, 10 years is an eternity and you got your moneys' worth. On the other hand, the Gumby suit will never be used. Replacing the drysuit, well used, after a decade is a far better value.
2. GoreTex for dive suits is rather silly. Agreed.
3. Foamed neoprene is durable--I have some ancient wet suits that are fully functional--but as a deck suit material it is useless.
4. The "no comparison" statement is simply bold, unless it applies only to dive-type dry suits. Dry Suits and Immersion suits are obviously related, and some have evolved to be virtually identical, since there are jobs that require survival protection you can work in.
There are 3 core questions:
1. Is a dry suit practical as cold weather deck wear? Many professional sailors feel the answer is yes.
2. Given the budget choice between dry suits and gumby suit, which makes more sense? Gumby suits are a little cheaper, but a drysuit is far more likely to save your life (MOB seems much more likely than sinking, though I have no measure of how much more likely). You can, of course, take both.
3. How do dry suits compare, according to the CG criteria? Some things will be failures (1 size fits all, durability in diesel), some will be passes (water exclusion, mobility), some will be conditional pass (wear a PFD, shoes, gloves, hood), and some would be interesting to see (righting, buoyancy, warmth--I'm just not sure, not having worn a gumby suit).