I'm a little sick of running in circles here. So, let's summarize.
We have three members of the Galaxy class that we know were destroyed. We have the Enterprise-D that's maybe a lemon based on certain writing concessions on TNG and was ultimately destroyed via a loophole in technology. We have two sister ships (Yamato and Odyssey) that were destroyed due to non-design related issues (computer virus and kamikaze).
We have at least nine other members of the Galaxy class that we saw fighting the Dominion. We don't know how well or how poorly those nine did, because we only saw them for roughly five minutes of screen time, but in that time we didn't see any shredded the way we saw Excelsiors or Mirandas shredded. We also know that at least five Galaxys were still around by the time of VGR's "Endgame" (and all in the Sol Sector, no less.) We also don't have a class that can be proven to be a literal replacement for the Galaxy class either.
So, still, all we have is one ship (Enterprise) that might have been a lemon but which we know in the real-world to be the victim of "convenience writing" on TNG and whose destruction was the result of the producers desire to destroy it, another (Yamato) that was killed due to a computer virus, and another (Odyssey) that was killed by kamikaze for the real-world reason of making a dramatic statement on DS9. We also know that, out of a possible minimum of twelve that might have been built, and an at least nine that survived, at least five survived the Dominion War. (There were a lot of ships sunk in WWII, by the way, that weren't considered "failures.")
Consequently, there's no proof that the class was an absolute success or a failure. An absence of proof of success is not proof of failure, and vice versa. We just don't know. Personally, I don't buy into most of the evidence of the class beng a failure because we know it has real-world dramatic reasons behind it.
I'm also inclined to believe that having five of them in the same place in "Endgame" is proof of something - either that those five were getting major overhauls (perhaps being finished, as part of those six that were rush-constructed to fight in the war with a lot of their volume empty), or that Starfleet built more than those "other nine."