That has not been my experience. When people move their head the same way, every time... I find it just as easy to hit them as it is to hit people with no head movement.
That said... head movement was not the point of this exercise. Not all exercises have to be about head movement. Boxers do sit ups... I have yet to see one effectively use a sit up in a fight. They jump rope and use the speed bag as well... but never seen those show up in the ring.
Interestingly... when I did go to a boxing gym, to box... we started out doing footwork exercises. We all lined up and the coach would have us all step forward, backward, left, right... as he called, keeping out hands up. When I was a beginner, he was not teaching bobbing and weaving in that exercise... but was teaching foundational movement.
When I trained MMA, we would also do footwork exercises, though the stance was a little lower and the feet wider apart. MMA has to worry about take downs and kicks, as well as punches. So it makes sense that they move a bit different than an art the only works with punches. But again, we did foot work drills that worked only on the foundational movement. We did other drills that worked in other things.
The idea is that different exercises build up different things. When people look at TMA, they complain that certain drills or exercises do not show up, exactly as practiced, in a fight... even though the things trained by those drills and exercises do. The same people look at MMA, boxing and wrestling... and completely ignore that fact that these arts also have many exercises and drills that do not show up in a fight... however, the things trained by those exercises and drills do.
Just because I prefer one way to train... does not mean I have to object to and argue against the way someone else or some other art trains. That kind of training just is not for me, but if others get something out of it, great. In actuality, I like to try all kinds of different ways to train. I usually find, that if I humble myself, put time and energy into training and really evaluate what the training is doing to me... that there is value in most ways of training. Sure, I find many times when people miss the boat, and don't see what a certain thing is teaching... or maybe I just see things a little differently, maybe I am the one missing the boat... But I find it worthwhile, to try different ways of training and love to try different arts. Even when I don't stick with an art... I usually find that I learn new things, that I can study in my own art and in the exercises and drills that work for me.