The ds9 technical manual is not really something you should consider 'canon'. I mean they couldn't even write the excelsior length correctly (i mean 500m++??? Most of us know its around 467m).
The cardassian galor is actually quite an old vessel and was not really a threat anymore towards the galaxy class vessels in the next generation time. Clear examples were seen in "the wounded". A galor shoots multiple times with full power and the enterprise D wasn't really damaged. One shot was fired and the galor already stopped. Same counts for the phoenix who destroyed single handed a cardassian warship, despite the galor had the transponder codes. (probably a galor destroyer or warship).
There were three types of cardassian galors, type 3 the most powerful one. Could be something like the miranda vessels (one was a transport vessel/medical vessel and that's the one without the rollbar, one with the torpedo launcher and thats type2 and let's say type 3 like bozeman or the saratoga. I'm just giving examples here).
The galor were beefed up extremely because of the dominion. They helped them building way more powerful ships and putting more power in their weapons. Remember the beginning of way of the warrior? THe klingon fleet just swarmed through the cardassians like they were nothing despite even that the cardassians in the end had the ability to form up a fleet. When the dominion was there, we saw a galor firing one shot on a bird of prey and boom... Same for the the end battle, one shot and a dom fighter was destroyed (could be it was already heavily damaged of course, and they had their weakspot above).
TNG galor-> weak
Dominion shows up-> quite powerful.
the reason the honsu was exploded was pure of the story. They took the model because a designer was making the nebula in cg or something i've heard.
