Way more than I felt like responding to on my telephone...
I suspect you're thinking of Rory MIller -- but you're not really understanding his point. A block-then-strike approach is going to be behind the curve, and getting further and further behind, UNLESS you do something to change catch up and pass your attacker. What do I mean by that? If I wait for you to punch me, then I try to block your punch with a classic up block found in many martial arts, for example, then try to punch you after I block you -- the odds are that I might get the block in, but you probably won't be standing there for me to hit you afterwards. Instead, you're throwing your own second shot, moving, etc. And I'm already behind the curve to start with, because I'm waiting for you to act...
Yet the principle of defensive fighting is found in many martial arts which have stood the test of time...
H'mm... Maybe there's something not being shown? Maybe we're missing something...
Different styles have different answers, but here are some parts of my own answer... First, I don't wait for a strike to defend myself. As soon as I perceive that you're moving to attack, I'm doing something about it. I'm taking a defensive step to point that will give me an advantage. I'm preparing a "block" that does more than merely stop the strike; it inflicts harm on the incoming limb, it disrupts my opponent's balance, impairing their ability to throw another attack, and it's stopping the strike, too. Then I'm moving into some "doing unto" while my opponent is recovering...
Of course, this sounds easy. Hell of a lot harder to do than describe...
A perfect move, as Rory and several others describe it, improves your position, worsens your opponent's position, prevents them from harming you, and delivers damage. (I've reordered them reflecting my own emphasis... I have a lot of options if my position is better than my opponents...)