This one's really just a thought bubble on my part.
One of the interesting continuity points in TNG's first couple of seasons that I really liked was that the crew weren't entirely sure they'd figured out all the kinks in the Galaxy class. It seemed to be strongly implied on several occasions that the Galaxy class was an experimental ship and that thy're kinda still figuring it out as they go along. Isn't there dialogue in "Contagion" along the lines of Captain Varley of the USS Yamato
stating they should have run more tests on the Galaxy class before sending them out?
said earlier, Varley's comments weren't supposed to be taken seriously. He was frustrated because of the Iconian computer virus or program that would have felled any starship design (the Yamato
was lost before the virus was discovered, IIRC, and LaForge subsequently ruled out a design flaw)
Otherwise, the Galaxy-class starship was the newest and most advanced design at the time and had likely underwent many years of testing.
And while the Yamato might be chalked up as an isolated incident, there have been a surprising number of Galaxy class ships that are seen to go up in flames on-screen. The Odyssey was taken down very quickly by Jem'Hadar attack ships (admittedly Starfleet wasn't prepared for the weapons they were packing), but even Enterprise is shown to have a very specific achilles heel: the coolant system, which faults while battling Klingons in the alternate universe in "Yesterday's Enterprise", and then does so again in almost identical circumstances in "Generations". And on neither occasion can Geordi LaForge actually do anything about it. Once it goes it goes, and they seemingly have no options left but to evacuate the ship.
One can't help but wonder if all the talk of the Galaxy class being untested might be true? They do often seem to be more fragile than maybe they should be.
Only three Galaxy-class ships were lost. In comparison, Starfleet likely lost many more Oberth-, Miranda-, and maybe even Excelsior-class ships over the years, and yet those designs were still around by the late 24th-Century. There's nothing really to suggest the Galaxy-class is fragile at all and I would argue it's one of Starfleet's strongest
But I don't think any starship design is invincible and none will ever be.