Why does well designed = bad tone? The plugins they've released so far sound amazing.
Ahh.... inbred prejudice on my part
You are correct. There is no practical reason to believe that a nice GUI would indicate bad tone.
As for the OP,
While I do use the Green Scream sparingly, the stomps do need a little TLC. It isn't that they are bad (really nothing in the KPA today rates "bad" to my ears), it is just that the verbs and delays are so great that you kind of expect the stomps to be world class as well.
I personally find it hard to imagine replacing my KPA. I paid top dollar for a top of the line product. I expect to be using it 10 years from now.