While I agree that simplification does have its merits and elegance, the STAR TREK franchise ("canon") established a while back that there are different spacecraft designs applied to different tasks, especially in the Federation Starfleet. Even the combat-obsessed Klingons appear to use multiple designs.
I am torn on this issue, though. TOS showed us very few ship designs, restricted by its budget. TAS and the movies began showing more. Federation starships shown in TOS were invariably cruiser-types like the Enterprise, using the same basic saucer-and-cigars-type shape. This works especially well if you think the entire Federation operates on only 12 or 13 starships.
But if you think the Federation of TOS is "bigger than that", and if you retcon in the possible existence of companion ship classes such as the Miranda, then it is possible to have a larger and more diverse fleet of ships engaged in a variety of roles.
Here's what we saw in "canon":
TOS Federation starships
Star Cruiser-type starships (Constitution-class?)
Space cruiser (Aurora)
automated ore freighter (Woden)
[other ship types were mentioned but not seen; including starliner Antares, U.S.S. Carolina, Cyrano Jones' one-man scout, old J-class starship, Class 4 stardrive vessel S.S. Beagle]
TAS
Manned Freighter (Huron, "The Pirates of Orion")
Automated Freighter ("More Troubles, More Tribbles")
Starship Bonaventure ("Time Trap")
TMP / Movies
Miranda (Reliant, Saratoga)
Excelsior (NX-2000)
Oberth (Grissom)
Even with some retconning, this simple list is substantial to begin with and the language used in TOS alone suggests that there are other types of ships operating. (Why call the Enterprise a "star cruiser" or "heavy cruiser" if there are no other Starfleet starships-of-the-line to differentiate it from?)
For me, the key word is "cruiser", suggesting a vessel "outfitted for a cruise", or sustained deep-space voyage. This meshes well with the Enterprise's five-year exploration mission. But it is also possible there are other starships in operation that not outfitted for a cruise, and are therefore not cruisers. (Miranda and Oberth, perhaps?) Plus the existence of freighters in both TOS and TAS suggests strongly that there are transport craft in the service of both civilian operators and Starfleet.
I've heard, but never actually read, that, in Stephen Whitfield & Gene Roddenberry's 1968 book "The Making of Star Trek" that Kirk was supposed to have come from a (non-canon) destroyer-type vessel as his previous assignment before taking command of the Enterprise from Pike. (Can anyone provide a page number for this, please? Thanks, and much appreciated.)
So, there's a list of TOS/TAS/TMP-era ship types, most of which have an obvious Starfleet nomenclature and others which possibly could.
The idea of a juggernaut one-size-fits-all starship fits well into the BATTLESTAR GALACTICA universe (original or Ron Moore-series), where the structure of the universe and the nature of travel are very different than TREK.
The idea of a "wedge" ship was briefly explored in Goldstein & Goldstien's 1980 book "Star Trek Spaceflight Chronology", which proposed that the Constitution-class starships would be soon superseded by a new generation of larger, much faster, uber-powered ships of a radically different design philosophy. It was a neat idea, and small hints of the concept seemed to make it into the NX-2000 Excelsior and Galaxy-class Enterprise-D, but the more radical parts of the concept were forgotten and subsequent movies and shows adopted a different philosophy.
I still agree, though, that the TNG/post-TNG-era proliferation of ship classes seems convoluted and chaotic. It could use some simplification.