> If the OP didn't like it because they don't like well done burgers in general then, well, I'm not sure what they were expecting when they ordered one.
What OP actually said:
"It's cooked well-done and can't be ordered any other way."
OP didn't order it that way, Umami Burger won't cook it any other way.
They said they didn't have any choice in how it was prepared, and the restaurant picked "well-done" — but yes, I would call that a success for Impossible. Just because Umami Burger prepares the burger poorly doesn't mean the burger failed, since it tastes as good as a normal meat burger would be expected to when prepared the same way.
If the OP didn't like it because they don't like well done burgers in general then, well, I'm not sure what they were expecting when they ordered one.