pretty much. generally it is assumed that the 2750 art was the appearance of the ship designs as they originally were built, but that by the end to the star league, thanks to design revisions, updated, refits, etc, you also had the 3057 art versions around alongside.
with the Clans having largely switched to the 3057 art versions when they upgraded all their warships to clantech specs.. since they were having to basically dismantle everything but the KF core anyway to install things like harjel and clan DHS based cooling systems, presumably they just decided to rebuild the superstructure and decks to the late star league specs in the process.
why they didn't go further with more armor, more guns, etc on some of then who knows. maybe they didn't want to change the plans too much from SL spec.