The Unifit equipped toilets work very well.
Your plumber is showing his inexperience.
The Vespin is considered an upgrade from the Drake, in that it comes with the easy to clean skirted bowl, and Sanagloss finish in the bowl.
If your plumber was not moving the roughin, you could have ordered the 14" Unift and that would have moved the bowl closer to the wall on your 14" rough.
The adapter is a lot less money than paying a plumbing to replace the drain.
But then, maybe the plumber looked at what you had, and thought it needed replacement.