You said they all use the same tweeters as if to imply that they all have the same tweeter response. The tweeter response however depends not only on the tweeter itself but also the cross-over frequency and the subsequent equalization.
Nope; only mentioned the tweeter cause you mentioned it yourself when you stated you returned your old QS4s.
Naw; I'm not the one who says they sound good together, cause I've never heard them. But Axiom felt that using the same tweeter throughout the entire audiophile line was important enough to remove the old hybrid tweet. But yup; how the tweeters fit each box and the mids is important for sure.
I'd really like to see a white paper with waterfall plots for all these speakers. That would be jolly fun!