I think it comes down to which modern boat we're talking about.
In the old days before computer simulations they built the
fiberglass hulls mostly to wooden boat standards because they didn't really know how strong it was or how long it would last. So they were much thicker than they had to be. Layups being equal that usually equates to a stronger piece. Nowadays they can make it thinner because they can model the strength it takes to do the job it has to do at that particular point. The only problem with that is that it's hard to model every
single stress situation that could possibly be encountered.
If you look at a modern
Pacific Seacraft or
Island Packet, you're probably looking at a pretty good sea boat. Hunter,
Catalina, and equivalents unfortunately tend to be on the more cost effective side. But that's what they're designed for and they do that job very well. I had a
Catalina 25 and it was fast and fun to sail. But knowing what I know now from years of sailing different boats and being in different situations I would never take that boat on any
offshore cruise.
The effect of having a strong boat underneath you isn't readily apparent sailing in protected waters. For example I remember once when I was 3 days out of Port Canaveral heading for Cape Hatteras in my
Cape Dory 28 and got caught in an unexpected fast-moving front that came down across the
east coast and hit me at ~2:00am when I was crossing the
Gulf Stream towards
North Carolina (I had sailed the Rhumb line from Port Canaveral to Hatteras). The
wind was blowing over gale force against the stream and the boat was falling off waves. I'm not talking sliding down, I'm talking falling off as the waves would disappear beneath her. Because of the press of
wind on her heavy reefed main she remained heeled as she fell and would drop onto her side. The waves were turmoil since the prevailing north-east running 6-foot swell was meeting the front-driven south-west running swell. Periodically 12-15 foot waves would spring up underneath her as the opposite running waves came together and then disappear leaving her floating in the air to fall back down. In all that terror it was very psychologically comforting to feel her solidly thud in a huge splash when she hit every time. I attribute that to her solid construction.
I can only imagine what that would have been like or what would have happened had I been in my friend's (2000-era) Hunter 25 that would oil-can even in light intra-coastal chop. Maybe it would have been plenty strong enough to survive? Who knows?
I don't have experience with the larger Catalinas, Hunters, and equivalents and maybe they're a different type of boat from their smaller counterparts.