Exactly true...I have hard time accepting that K'tinga and D7 would even be different classes, instead of minor variations within a sinle class, let alone that they would be different sizes. Original Connie and the Refit are more dissimilar than TOS and movie era Klingon cruisers. I think that it is just a single class, Klingon name being K'tinga and Federation designation D7.
If you scale them to the same size though, the proportions of various sections are quite different between them, much in the same manner they are between the TMP Enterprise and the TOS Connie.
It's really unreasonable to treat the "refit" and the "TOS" ship as "the same ship" in any PRACTICAL sense. (I suspect that a few components were left "original" during the total-reconstruction, just to avoid being in total violation of some diplomatic agreement.) They are, in every meaningful way, two completely different vessels.
The same applies to the D-7A and D-7M classes. They "look the same" and I'm sure that some fairly irrelevant components were kept the same in the secondary crew messhall worm-and-lung-refrigeration unit. But it's really a totally new ship, with totally new capabilities.
I see the TOS ship, the D-7A, and the TOS ship, the Constitution-class, as a special case, where there was some sort of treaty between the Klingons and the Federation limiting the number of "new hulls" which could be constructed in any timeframe... and I see the D-7M and "Constitution refit" designs as being parallel "sneaky" ways to get around that treaty.
That's the only way it makes any sense to me. They're too different, in terms of size, proportion, installed hardware, internal arrangement, and capabilities to be seen as "the same" if you're trying to treat this as a "real" universe.