Also, the Federation could be a lot more decentralised then todays … arms-bearing organisations. Not only the very different demands a so big space could on many different designs – also many different shipyards could develop many different ships.
Also modern navies simply don’t need to be churning out new designs every 5-10 years. I mean the USN reigns supreme and no one is seriously challangeing that things are, historicaly however VERY differant in a situation where you have a naval arms race.
If one looks at the navies of the great powers in the first half the the century you see an aweful lot of ships being built with regular new classes, between 1905 and 1916 (the period of the dreadnought arms race) the UK built about a dozen seperate classes of capital ship (battleships and battlecruisers)
the US built 7 classes, and the Germans 5 classes.
during the 1920s and 30s we nearly saw another massive building spree again that was only stopped by the Washington Naval treaty. It should be worth noting that during WW2 the US navy had over 50 differant classes of combat vessels operating at the same time. I’d say what doesn’t make sense is how few designs the Klingons and Romulans have (the Romulans DESPIRATELY need some sort of medium weight workhorse ship)
I think that there were at least three eras in which at lot of new design were commissioned:
- In the 2250s after the Federation-Klingon War which clearly showed Starfleet that most of its designs had become obsolete
- The late 2760s / early 2370s in which a lot of new designs were developed because of the Borg threat.
- The huge losses during the Dominion War led to another nearly complete rebuild of Starfleet leading to the decommission of all of the old designs and to the development of new designs.
During the whole century between TOS and TNG only a few new classes were commissioned and most of the ships of that time were still active in the Dominion War. Leading to the situation that there were really a lot of classes with vastly different capabilities for every single role.
DIS explains quite well why the Klingons only have so few designs. before the Federation-Klingon War every house had its own fleet and its own starship designs. This changed after the war and the introduction of the D7-class. We still do not know much about Romulan starships and thus we cannot say how many starship classes they have and how often new designs were commissioned.
Multiple ship designs create personnel and logistics problems.
Crew gave to become familiar with a new design. Not just command crew and the ships’ capabilities, but lower decks crew…. Where are the vaccine suits stored? Where are the damage control lockers? Where do the power conduits run? How does refueling and reprovisioning work?
It takes months for new submarine crew to earn their dolphins in the US Navy, learning the damage control procedures, deck layout, etc and being able to do certain tasks in the dark, by feel.
Starfleet likely has similar requirements.
…and now when a crew member transfers to another ship, they have to learn it all over again…. And Starfleet has 371 distinct cruiser designs alone? If a crew member takes six months to become fully functional on their new ship, and they transfer 10 times in a 20-30 year career, that five years that they are performing sub-par.
The US Navy, the largest navy in the history of the world, has essential one design for each class of ship. Even at the height of the 600 ship navy there were maybe 2or 3 types, which were mainly just variations of each other and some legacy hulls.
Logistics are also problematic. Spare parts for all these ships can’t all be replicated, or they would just replicate entire vessels. How to fix them, as well as what to fix them with, also becomes a problem.
great wok on all these ships so far just saw that you put the ,
Larson-class destroyer up as well came out really well. 
You should check out my starship sheets here. The Larson (both the TOS and TMP versions) is in the Federation Starships folder, listed alphabetically.