This does read like a claim that everything contained within a martial art 'works' (aside from chi balls).
For there to not be a 'whole lot' that doesn't work, given the scope of the combined syllabii of every martial art we have, would leave the greater majority of all of it as effective.
The important part is the last part of what I said - "if correctly applied". That goes for not just the techniques, but the concepts and training methods as well. If a training method is not correctly applied, then the training method is flawed. For example,
- Techniques: Cartwheel kick. If you do not know how to cartwheel or how to set up this kick, it is flawed.
- Concepts: Escape a wrist grab by pulling thumb-to-thumb. I gave the example earlier that the concept was not understood by the MMA fighters, and because the concept was not correctly applied, it did not work.
- Training Methods: 1-punch drills. If they do not escalate in resistance, then 1-punch drills are not correctly applied.
Another key phrase is "widely taught." Not things that are fringe techniques or "Rex Kwon Do" type of moves.
Something I have learned from watching videos from many arts, in addition to training from my own classes, is there are a lot of things that seem like they don't work until you understand them completely. For example, the first time I saw a cross-arm Z-lock in hapkido, I thought "that's fake." Then my Master performed the same lock on me, and I quickly realized it wasn't fake. Over the course of my hapkido training, I've experienced several similar moments:
- A technique that "doesn't work" until I learn the proper footwork. (Using my footwork to do the dirty work for me works in most cases).
- A technique that I "can't get the right grip" until I learn other ways to do it. (For example, I couldn't get a grip on a V-lock because my chest was in the way, so I just pushed with my chest instead of my hand).
- Finishing moves that "don't work" until I can learn which angles I need to be at for which grips I have.
Every new technique that my Master teaches me is something that "doesn't work" or is "more complicated than it needs to be" or is "not as effective as an earlier technique", until I learn how to properly apply it. In fact, today I learned some of my blue belt stuff (out of 7 belts, I'm 2 away from black belt), but I also learned several things about our white belt techniques. It's humbling and empowering at the same time.
Coming back to your point, my original concept isn't so much about the moves themselves, but the attitudes towards them. If I gave up on these techniques before I learned how to correctly use them, then I would not have learned them. Or, if I would have looked at other martial arts and scoffed at their techniques, I wouldn't have learned things in these types of discussions.