I understand that it's not easy to design, but it doesn't seem fair to quote cherrypicked measurements from an entirely different speaker (e.g. this 7" mid + RAAL speaker you quote), as part of a critique of the Sierra 2EX, or RAAL speakers in general. That would be like me finding a poorly integrated speaker using the same woofers as one of Revel's speakers as evidence against that woofer or speaker. That makes no sense.
The Sierra 2EX is a different design than your example, and measures extremely well. If a small dip exists off-axis near the crossover of the 2EX, it is perhaps more subtle than many of the on-axis imperfections
in your Salon 2 plot
. And we haven't even invoked the Sierra RAAL Towers yet, which pair 5.25" mids and woofers with the RAAL 70x20.
So, I get it, if you're saying it's hard to design such a speaker. No disagreement that it's hard to get right. But that's not a surprise at all: Of course exceptional speakers are difficult to design correctly. This applies to everything in a speaker, not just any one singled-out component like a RAAL tweeter: waveguides are hard to design correctly, crossovers are hard to design correctly, ports are hard to design correctly, etc. etc. etc.
But clearly it is possible to design exceptional speakers with RAAL tweeters, and this is proved by the existence of such speakers. If the 2EX doesn't convince you, certainly the Sierra RAAL Towers should, at least.
Even if we're talking purely about the Sierra 2EX vs other speakers (like the KEF R3), the question really becomes about whether a subtle dip in the 2EX extreme off-axis near the crossover makes for a worse, or better sound than a speaker that also dips off-axis near the crossover, but never recovers (and continually decreases into the treble extension). The blind tests from me and a few others continue to provide evidence pointing towards the idea that broader dispersion is preferred, among these two choices.
It's natural to still be skeptical of course. That's why I plan to continue gathering data. Next up is the Neumann KH120, and after that I will probably test a number of Revel bookshelf speakers.