Oh sure, I'm happy to say that the klingon ships are durable. Don't get me wrong, I just think you can say this of a lot of Trek ship designs. The Federation has durable ships as well, or designs they've used for almost a century with no problem.
By the way, the K'vort and the B'rel are actually identical if you go by a canon-purist interpretation of the onscreen visuals. The K'vort only appears once in an alternate universe (although it IS mentioned in DS9, but again only once and we don't see it onscreen) in the episode 'Yesterday's Enterprise'. Fast forward to 'Rascals' TNG season six, and we see two B'rel class BoPs attack the enterprise - all the vfx in this battle are reused from the 'Yesterday's Enterprise' battle, meaning the B'rel per onscreen canon evidence, is the equivalent of the K'vort class. (also, it's rather difficult to imagine two scout ships pwning the Enterprise, any more than it is to believe that Lursa and B'etor could do enough damage in one BoP, but... wait, I think I just shot my argument in the foot there... -_-; )
Bear in mind that the whole 'b'rel is a scout ship and the k'vort is a large, upscaled cruiser-sized bop' isn't canon at all - it's Michael Okuda's interpretation of events. But I'm not really all that much of a purist - I think the BoP visuals have always been wildly inconsistent and the scaling varies so much episode per episode that there likely would be multiple variant classes of the BoP (indeed, that's basically the only in-context reasonable explanation for what is essentially an out-of-universe vfx issue). I can hope that the TNG-R project might settle this but I guess we can only wait and see.
I'm happy to accept whatever source you want to give me, but I don't really believe in this 'soft' canon 'hard' canon divide. There really is only one canon policy, so even stuff like the TNG and DS9 technical manuals aren't even canon, despite the fact that Okuda and Sternbrach worked on the shows in question. That's not to say I would reject whatever non-canon source you have, but I would rather it be proved by using canon sources over anything else. (in other words, I would consider something from a book to be persuasive, while something from an episode to be definitive)
There was a WestEnd games Book If i rember the Publisher correctly that had Various Klingon Ships the Excuse they Used for the D-7 was it was a Good Ship and that why it has been used So long. It was in R/D prior to the First Voyage of the Enterprise. Now I wont say its Conon but they guy who Helped write the thing was Named Eugene and Last Name was Roddenberry. So id put a little Faith in it. Wish i had the book still prob worth a bit of coin!