I think it was the validity of forms is backed up by bunkai.
I haven't really ever seen bunkai trained in alive enough manner to satisfy me. Not in the same way that you could equate sparring to.
Contested,unpredictable,contact. Those sorts of things.
The closest I have seen to the description of an alive contact bunkai would be a kickboxing Dutch drill. Which is of course not bunkai and does not stem from kata. And is still a drill to a certain extent. It plays its part but is not an alive test.
It isn't too difficult to find a school practicing bunkai like that, that's how we do it at our school
Beginners do only one step at full speed well within range of getting hurt,
Then as they get used to that they start doing them on an opponent attacking in more of a boxing style, and having their partner come at them with a certain technique.
Bunkai Practice is Drilling,
Just like the kind you'd do in an MMA gym,
But it isn't sparring