I'm probably going to go into classification schemes in a later chapter (particularly the 24th century ones), but I do agree that Starfleet's much more likely use a classification system based on roles rather than sizes.
OTOH I'm a bit loath to believe ships like Kelvin
are stupendously larger than Starfleet's "ship of the line" like Enterprise
nearly 3 decades later. I do think that the later Abramsverse ships gathering for the Vulcan expedition make a better baseline for comparisons than the licensed/fanon designs. I also think expanded secondary craft capability makes sense for something like a survey ship. Given that Starfleet's missions within Federation space are more likely to involve things like humanitarian assistance, infrastructure building and surveying existing star systems, ships that are of moderate size that can pack lots of auxiliary craft make sense.
One thing I think to bear in mind is that purpose built military ships usually make lousy exploration or even surveying vessels. Most of the major research oriented naval ships in the 19th century were either based on sloops (a size-class smaller than cruisers like frigates), or were of non-military ships like luggers or whalers. The famous ships of James Cook like Resolution
were based merchant colliers with substantial modifications to their hull forms, rather than using a military post-ship.
On the other hand, the way technology in Star Trek seems to work, the things that make a ship an effective explorer also tends to make them very effective tactical vessels. Size seems roughly to be correlated with both speed and power generation capabilities, along with endurance and mission payload. Smaller purpose built warships also exist, but with a handful of exceptions don't seem nearly as capable as the much larger ships built with the same technology. Defiant
for example might be a very powerful warship, but despite that the way the battle in First Contact is depicted, the Enterprise-E
appears to be a vastly superior ship.
That is to say, I'm torn. I think the realities of the mid-late 23rd century did force a lot of compromises on Starfleet that were later rectified by a combination of technological progress and the ability to plan. The SIF + modular interiors I think helped them focus on expanding capabilities rather than designing new hull frames, and the newer designs with their emphasis on greater surface area/volume seems to imply attempts to take advantage of those technological traits.
Once we get into the 2380s, I think this changes again because Starfleet begins experimenting with Quantum Slipstream drive that requires radical new hull forms.
As a side note:
My drawing from naval history/literature is generally drawing more on Age of Sail/pre-20th century naval history than anything modern. Part of it is just preference, I find that period more interesting. But just as much has to do with the technological realities that Starfleet seems to face being more akin to sailing navies than modern ones. As such the gap in capabilities between say a very large ship and a somewhat small one is probably smaller in my estimation in terms of TACTICAL capabilities than they are in other areas like spacekeeping and endurance, not to mention flat out speed. In this case I tend to think of Defiant
as being a small sloop equipped with the equivalent of very large carronades or maybe rifled shell guns. Perhaps with some armouring to let it actually survive contact with a larger ship.
When I use the term "Frigate" I'm thinking more of "multi-mission ship smaller than the main line combatants" rather than "ASW Escort". The only reason I don't use "sloop" is because it's never used in canon!