I'd just like to point out that the Constitutions in their day were considered supremely tough and yet (according to the lore) Enterprise was the only one of the original 13 to survive to ~2270, when she put into San Fran for her refit. Given her generally accepted launch date of 2245, and that she was the first built of the line, that's 1 ship every ~2 years on average. (though we know that several were lost in rapid succession between 2265 and 2269).
Of the 12 known or postulated Galaxy hulls, 3 were lost in the first 7 years of the class' service. That is approximately the same average rate/year as the Connies.
Not too shabby.
Also, remember the original project plan for the Galaxys was 20-year deep space exploration unsupported. That's why they were so big, so luxurious, and included families. They never got to be used for that purpose, because the Romulans re-emerged, and they discovered/were discovered by the Borg, etc. Starfleet apparently made the call to keep them closer to home in case they would be needed.