Personally, I'm kind of mixed. I generally have tended to regard them as essentially being the same design, and I don't consider the TMP modifications to be that great of a chance compared to how the Enterprise was updated. I recall hearing at some point that one reason the movie Enterprise kept the "Constitution class" moniker was at Gene's insistence, because he didn't like the idea of "replacing" the original ship.
However, that being said, I recently have been getting some of the old FASA stuff and I'm a bit more comfortable with the D7 designation being the specific type, and the two versions being separate models of that type. FASA said that the K'Tinga name only applied to one specific model, and that other variants had different names. I've seen the names Klolode and Klothos suggested for the TOS model, so I don't mind including those as specific variants of the D7 class.