On the other hand, what we see done by the Enterprise
may also be grunt work of sorts. Nothing precludes the existence of even more glamorous and perhaps larger ship types that don't run errands in extreme deep space, but rather concentrate on winning decisive battles or representing the UFP in the best possible light on diplomatic cruises through luxury and splendor unavailable aboard the Enterprise
As for using those Antares
modules for varying tasks, "Charlie X" almost spells this out for us: Kirk wavers between considering the Antares
herself a "cargo vessel" or "transport ship" and "science probe vessel". The latter role is supported by the fact that this humble freight-runner made a mysterious diversion to Thasus, where supposedly there's no freight to be picked up or delivered. Perhaps some of the modules on the Antares
(say, the entire crew compartment) were UE Space Probe Agency add-ons that turned this otherwise standard automated cargo drone into a secondary survey asset?