...But the Reliant
does have mass/volume comparable to Kirk's ship, and seems to feature all the bells and whistles as well. She's just put together in a somewhat different shape. If the extremely subtle differences in size or equipment are indeed significant, then all bets are off as regards Starfleet ship type designations. Would for example the fandom Belknap
qualify for a cruiser when her secondary hull is smaller than that of Kirk's ship, while her neck has greater chord? Is the Constellation
not good enough for the cruiser designation due to the lack of a secondary hull, when she otherwise would seem to outbulk Kirk's ship by quite a lot?