I disagree and here's why. The entire point of a compromise is to move off of your position towards the other side.
Here a player wanted a turtle person including visuals. That can't fully for reasons, so the DM offers the compromise of being the turtle person in all but visual. Now the player has the option to accept that compromise and move off of his position to having a turtle person, but that turtle person doesn't look like a turtle. If accepted, both parties have moved off of their positions towards the other side and met somewhere in the middle, in this case almost all the way to the player's side of things.
It's not capitulation to move towards the other side part way. That's by definition compromise. Capitulation is giving in 100% to the other party.