It is my opinion that the Ambassador Class ship should be its own ship and not a skin for the Galaxy Class ships due to the fact that the Ambassador Class ship is indeed smaller.
I believe the developer team is having a difficult time differentiating it from the Galaxy Class. Therefore, I think we need to do some brainstorm for this ship a little bit.
FACT: The Ambassador Class ship was a peacetime ship. Therefore, I think a neat perk idea for this ship would be for it to come with a very rare and two rare diplomat duty officers.
FACT: The Ambassador Class ship came before the Galaxy class. Therefore, I think that the Ambassador Class ship should be the same Tier if not the Tier below the Galaxy Class ship.
Due to the Galaxy Class ship being classified as a Cruiser, I think that the Ambassador Class ship should be classified as a Science Cruiser. This would in affect make the ship lean toward the science ship type but with a hint of still being a cruiser. This would make it a little different from the Galaxy Class Cruiser.
In the TNG show, the Enterprise -C took quite a beating. I think it would be neat therefore to show it is a tough ship by giving it a +10 passive bonus to its shield power setting.