No, not to the extent that myopic Brent would have you believe. There are boats with the odd leak. My Valiant 40 had a leak in the foredeck hatch, right over the V berth. I kept my dink stowed over the hatch. That cured it. Chainplates can leak a bit if not sealed properly. I've never had a chainplate leak and I've only ever owned grp boats. My Esprit didn't leak. The mighty PERRYWINKLE did not leak as long as I dogged the foredeck hatch down correctly. But this had zero to do with grp construction. It was just an odd Scandinavian alu hatch.
I have found that most leaks are due to improper bedding. Remove the piece of hardware portlight, etc, re-bed it and there you go, good as gold. Spike removed the handrails on the house top so he could varnish them. When he reinstalled them he did not bed one leg down well. It leaked. Not much but a bit. He took the rail off and re-bed it and it was fixed. It was an easy to locate leak.
I have known some poorly built boats to have hull to deck joint leaks and these can be a real problem. When get a leak like this it doesn't drop down where it comes in usually. You may have a leak up in the forward quarter of your rail but the water will run aft to the low point of the sheer before dripping. This can make finding the leak problematic. But this is a poorly built boat. Think of the problems you could have with a poorly built steel boat and we have all seen those.
Brent gets desperate (oh really?) and gropes for anything he can grasp to attack any boat that is not welded steel. We might as well get used to it. He has very little experience with good grp boats. I would imagine he has never spent any time on a quality grp boat. He will say he has but we know he fibs. His converts come from cheap, crummy grp boats I suspect. They just don't know any better. Brent gives them a cheap boat that doesn't leak and has a companionway door that looks like it came off a Fridgidaire.
A friends Crown 28 didn't leak last year but sure does this year. fortunately he has ben able to move aboard a BS 36. Another friends Hughs 31 leaks a lot. Removing the entire toe rail to find the leak then rebedding it, is no small job.
Another friend spends $280 a month on oil to keep his Ericson 37 warm. Sure you can make a GRP boat watertight, and comfortable ,but don't assume it will be when you buy it.
One should read about Hal Roth's experience with a decorative wooden toe rail ( attached by dozens of holes thru the decks)while crossing the North Pacific, before getting too impressed by such an arrangement. The difference between what he did to rectify the problem, and those who advocate such style over substance, is cruising experience.
Several years ago the single handed transpac was won by a guy from Seattle, who lived aboard his boat. Guys from sunny California were soaked by deck leaks the whole way across. The guy from Seattle was warm and dry the whole way. The reason was, that by living aboard in rainy Seattle, he had found and dealt with all the deck leaks over the years , as they appeared. The guys from California had not seen any such rain, and not having lived aboard, the automatic bilge pumps had kept them naïve.
A GRP boat can be made watertight, and insulated, but don't expect that from a boat which has not been lived aboard for a while in rainy climes. Bolt down hardware can be watertight, for a while, but it has no comparison to welded down hardware or welded metal bulwarks, which will never leak . The best, most reliable bedding compound ever invented is welding. It never needs rebedding.
Hull deck joint leaks are from underestimating the loads on such joints; they take almost the entire twisting loads on a boat.
Putting a dinghy over leak is not a solution at sea, in rough weather. Perhaps that is what the guys from California did, to avoid having to deal with it in port, only to find out later it doesn't work so well underway .
My one piece aluminium hatch has become standard on round the world racers, which don't use teak sliding hatches and drop boards, for good reason . It is water proof and airtight in all conditions( Good seamanship)
I've read of people inside, in front of drop boards and sliding hatches in a gale ,taking a shower of spray thru them every time wave hit, like someone turning the shower on and off every few seconds. Accepting that, for decorative reasons, is simply bad seamanship ( and not all that bright either.)