I believe PD was using the example of the ballet dancer to illustrate the need to basically stand up straight and maintain that by use the core in order to spin properly. I agree that other ballet techniques don't work/is counter-productive to partner dancing but I don't think PD was pushing those.
My post was very specific. The "only" assertion has to do with tucking the butt under the torso and using the lower abs to position that portion of the body "straight." The Ballet/Jazz/etc. solo dancer in the video demonstrates this nicely. It's amusing how other readers infer from my claim all sorts of gobbly gook, like dancing from the core, which is _not_ the gist of this "positioning" issue. For all decent classical dancers, this is a given.
Most/all of my other statements/claims are in support of the main assertion.
My single/main assertion goes beyond just maintaining the tucked butt for spins, which is probably what many dancers do (only). I assert that for most if not all of partner dancing, the butt should be positioned (roughly) thus because the "straight" lower back allows superior movement. This includes in doing walks, rocks (as in the Samba example video), leans/sways, fans, whatever. Note that in my analogy of the "flexed" chopsticks when the tucked butt is deployed, the body itself may not be rigorously straight (note "with flex"), as there could be a (single) curvature of body (from foot to head, as with a tree blown by the wind). This is simply physics, and I can elaborate more later.
To me, technique is technique, independent of dance (the idea that a tucked butt is "Ballet/Jazz" technique is silly, as obviously many/most dancers do it when spinning in any dance, partnered or solo). Some techniques work in certain dances/movements (good technique) and some don't (bad technique). Certain dances expose us more to certain techniques, such as Tango tends to involve more fans (fan figures/moves), but these figures (and related techniques) can certainly carry to other dances, as in fans in WCS or Foxtrot.
Instead of hand-waving in contesting whether a particular technique is good or bad, especially when misinterpreting the original point(s) of my assertion, there is much more useful/productive ways of making points. I invite posters to make comments about the dancing/dancers in the Samba Closed Rocks example, being very specific and indicating time in the video, since the posters seem to have so many strong opinions about techniques (in this case butt positioning). Show us what you know. I already stated some of my thinking, and can go into even more details later.
I have taken private lessons with only a few teachers.
I have taken 10+ years of privates and 20+ years of group classes (in Ballroom and many other partner dances), plus dozens if not hundred of coaching lessons, including with many top-ranked dancers in many genres. I would be surprised if any of the other posters in this thread has taken as many lessons or have come across as many varied instructors/coaches as I have. A very few may have spent some $$$ more than I have, but probably in areas (costumes, comps, etc.) not related to lessons and learning. Unfortunately, as human nature would have it, (other) readers jump to conclusions about what I stated, twisting my words from not reading carefully. They can certainly believe whatever they want, including dancing with a protruding butt, but their assuming things like I haven't "heard it all" is amusing. I deliberately use words like "lower abs" and "butt tuck" to stay away from this over-used idea of "core" (what is that? a lump of the entire abdomen? the entire torso?), and yet readers assume based on their own stories.
I re-iterate that in the thousands of lessons I've taken in partner dancing, I've never heard one instructor mention the importance of tucking the butt, the one technique I believe is fundamental to all partner dances I do (about 35 of them). I'm sure some/many of the instructors do in fact tuck the butt at times, or perhaps most/all the time, especially when they spin, etc. but they may not recognize its (all situational) importance and convey it to students. I have to stress, as I had already mentioned in the need to refine, that the "tucking" in partner dancing is not quite exactly what the Ballet dancer demonstrates in the video. I'll get into this later, as it gets protracted, since this and many other great techniques that derive from it are highly intertwined.
The posts from other readers actually support my claim that no/few Ballroom/partner instructors ever teach/mention butt positioning (from what I can tell reading some posts, some instructors may even teach/espouse/do butt protrusion). The posts keep mentioning some ethereal concept of "dancing from the core" which is so vague, it's useless (and not what I'm describing). Very similar to what I hear from many instructors about "body leading," when many of them that claim to teach it have no clue how to do it well. There's a big distinction between never having heard of the specific technique verses having come across it (heard about it or figuring it out) but discounting it (for oneself, or for all).
BTW, discussions about specific muscles, etc, is really pseudo-science to me, where dance instructors pretend to be surgeons. Dancers need to know much more general and practical information, such as the lower abs are far less strong than the butt and thigh muscles, and hence should be used more for positioning than powering.