Thiel Owners

That's why I think either approach has its merits.  To say one is "better" than the other is missing the point.  As I also said in my previous posts (many posts ago), high-order speakers such as 24db/slope tend to have more "slam" vs. first order speaker, but on the other hand, first order speakers have a certain naturalness that not found in higher order speakers.  

The differences are subtle, but important.  

Thiel
https://www.youtube.com/watch?v=Jkf5uscX7Mg

ATC
https://www.youtube.com/watch?v=g_QsAlqTN_E

The two examples above are not "subtle" :-)

The sound clarify in the second one is far from natural and has much distortions. I like heavy rock but would not measure speaker characteristics based on that kind of music (even some early Black Sabbath recordings are better for this purpose).
There is no way to reproduce such recording naturally so it is hard to judge on speaker quality for that kind of recording, in contrary to the first one. 
Thiels never fail to reproduce naturally
human voice, in particular. 

Thiels never fail to reproduce naturally
human voice, in particular.

I would agree with that. On the other hand, higher order speakers tend to have some extra details or trebles on the voice that makes the voice "clearer" but not naturally. When you listen to a person talking in real life, you don’t hear the extra details that sometimes being reproduced by the speakers.  On the same token, when the drum beats, the higher order speakers have some extra sparkles on the top end that makes it appear to have more slam, but probably not there on the real drum in real life.  

But some people may prefer the extra slam and sparkle of the higher order speaker so it's not like one is better than the other.