Null tests don't directly mean that much to me either. But I don't think Kemper simply passes all other tests. It depends.
When I profile a source tone with gain, the end result will feel like there's a tubescreamer mixed in, to some level. I don't like this.
NAM doesn't do this (at least anywhere nearly as much), my own tonex captures do not when IK multimedia capturing works right (which is an "if").
On that end, I've done blind feel tests with many, many takes. It's easy to tell what Kemper is. Some other guitarists I've made these tests with prefered the Kemper feel. I do not.
That's part of why I gravitate to other solutions. But MKII may fix these inaccuracies, which is going to be a big one for some.