iii> Star Trek contradicts itself on a regular basis anyways.
3.0> This game takes place at least a few decades beyond the point that would be addressed in a tech manual, so whatever criteria that would determine if something was a CA or a CL (or I guess just a C? CC? By cryptics nomenclature) could easily have changes.... especially since it's such a an outdated design that is only kept in screaming distance of modern ships through many upgrades and refits, presumably.
The ship is 140 years old, so I agree that it should no longer be considered "heavy", however I think that they should slip the excelsior in there some where (mabe Tier 3) since it was bigger than the constitution and I'd love an opportunity to command one. (even if just for a while)