With some MA experience, one should be able to tell the application even from the solo move. But some solo move just doesn't make sense to start with.
What possible interpretation can this solo move be? It supposes to be a "double pulling" that you use one hand to grab on your opponent's wrist while use another hand to grab on your opponent's elbow. Since in this clip, both palms are facing down and also both "tiger mouth - space between thumb and the 1st finger) are not open (no grabbing intention), I can't map it into any meaningful application.
It's easy to see the application from the following clip.
In one sense I see what you're saying. For applications involving pulling or guiding the opponents bodyweight, the second clip looks, at first glance, more true to application, while the first might look more stylized. That said, I'm no Tai Chi practitioner, so I'm likely missing a LOT.
However, in the sense of discussing the application of technique merely by looking at the solo-person form (aside from excluding every one of the many arts that do not practice forms), this mindset of "one obvious, clearly illustrated application," is really quite style specific.
For example, in the Karate lineages, you'd be hard pressed to find a technique, pulled from the solo kata, which is identical in motion to its application. You'd also be hard pressed to find a technique that has a single, identifiable application. Karate and its offspring have very stylized, symbolic forms, some styles more than others, but I doubt there's more than one person on this forum that would claim that all Karate techniques are invalid. To say that a technique is invalid if the motion found in a solo-person form differs from the motion of the application dismisses three things.
- Any styles that don't use forms. Obviously, techniques are not only solo movements.
- Any styles in which the forms contain stylized or symbolic movements. (To various extents, Most of them!)
- The posibilidad that a technique may have different applications. Each application will necesarily have slightly different movement, weight distribution, power generation, speed, areas of body tension, etc.
This last one is the most important, really. Take your example of the rising block from earlier. (Note, descriptions that follow based on my own understanding/application; specifics not important!)
When the motion is applied as an arm drag and a rising forearm bash to the jaw, several things must happen. Significant torque must be applied to the grappled limb, powerful snapping force must be applied to the striking arm, and the weight must be solid, for the moment of impact, as well as a host of other small details. You will likely start and finish the movement in close proximity to your opponent, meaning the stance work will be somewhat stationary. The motion will also have large movements and take longer than in the second case:
When the rising block is employed merely as a ranged deflection of an incoming strike, the most important thing becomes speed and fluidity. Far less force is necessary for the rising arm to deflect a punch than to meaningfully strike the jaw. This will in turn affect stance and weight; instead of needing a solid, powerful connection, what is needed is fluidity and mobility, and the arm should be moving far more independently from the body. The other pulling hand is likely no longer yanking a limb, so it's hopefully doing something else, meaning it's
not coming to the hip as it was before, or at least not for the same purpose or in the same way, which will
also affect the rest of the body and motion. Obviously, everything mentioned previously about power generation (and thus overall body movement) is now null and void. The timing and footwork will also be different, as the rising deflection works best if you can slip in under the arm, closing with the opponent, and preforming the technique as your stance moves in.
As has been noted, by both you and me, a technique such as the rising block has many uses. Each of them is quite different from each other, when looking at the motion in application. And nearly every application is in some small aspect or twenty, significantly altered from the technique as found in formal solo practice.
My point being, that in most styles, it's simply not feasible to look at a motion, applied in a solo-person form, and then extrapolate from there its true application as well as its validity or lack of.
There are two basic ways to look at the question posed in this thread, "Are some techniques really valid or invalid?"
If by technique you mean "interpretable, solo-person formal motion, "Then the only possible answer is
"No, all motion of the human body likely has some application suitable for unarmed combat."
If by technique you mean specific
applications of a motion, then two things are true: based on the proven efficacy of the boxing right cross, it's clear that that at least one technique is valid and; based on the proven non-functionality of the aforementioned chi balls, there is at least one technique that is
not valid. So, for the second definition, it seems the only honest answer is
"Yes, not everything you can dream up will work, but there are some things that do work."
Which I guess implies that the only way to answer the question at all is to, as a group, pick one definition of "technique." I'd say that for the purposes of the discussion of validity, viewing techniques not as motions but as applications is both more functional and interesting.
