Spoilers Timeline of USS Franklin and Captain relative to ENTERPRISE (2001)

[Jedi_Master]

If you read Christopher Bennett's Rise Of The Federation novels, there's quite some stuff about fleet building, and at the point of 2165, the species making up the Federation are still using their own ships, with humans being the exploratory arm, the Andorians serving as the main combat ship, and Tellarites serving as cargoships and such. In the fourth novel, we're only now coming to the point where Starfleet is designing and building completely new ships. And that makes perfect sense.

Yep. I can see "Earth" ships being part of the Federation armada for some decades, even if they are given a new coat of paint and registry designation.