At least as far as karate is concerned, what were once practical movements invented in an environment where practicality was the be-all and end-all of martial arts have been interpreted, perverted, and watered down through the subsequent decades. Practiced correctly, the "traditional" blocks all demonstrate consistent themes about body positioning, movement, and theory that can then be applied in a more general way. But you have to start big and exaggerated and become smaller and more complex. That's how learning works. But instead of looking at it this way, many teachers these days teach only the shallow interpretation of the techniques, blaming their lack of effectiveness on "not being fast enough" or "not doing enough body conditioning."

Compare this, for instance, to traditional karate stances. There is no situation where it would make sense to be in a low kiba-dachi or low zenkutsu-dachi. But practicing the stances low builds the muscles that will make a shallower (and more practical) stance very strong. The exaggerated hip movements that come with practicing stances at that deep level can gradually become smaller and more nuanced as you pull the stances up.

Imagine that you'd never been taught multiplication, but instead learned to approach something like 5x12 by adding fives together over and over. It's not that it couldn't work, but there are much more elegant and effective ways to produce the same effect once you've moved onto more complex concepts.

It truly, truly bothers me how much stubborn and willful ignorance is directed towards the instruction of TMAs. They can be very effective if you're willing to analyze and develop them.

TL;DR The techniques aren't the issue; their instruction is. Good instructors will recognize what elements of the traditional blocks can be applied, rather than stubbornly teaching them in a shallow way.