This is what I told my son last night during training. He's too heavy in is stance and he doesn't have a lot of mobility. I told him that the stance he uses is for when he thinks someone will try to take him down. I used wrestlers as an example and how there stance is less mobile. Than a stance that is tall.
When we want to move fast across a distance then we stand up tall. (A person running)
When we want to be rooted to the ground and difficult to move then we take a lower stance (A person crouching or in a low horse stance, bow stance or cross stance.)
There's a different between quick mobility and light mobility. A stance can be low, heavy, and quick but travels very little distance. This is good for the majority of cases.
A stance can be light, fast and a lot of distance this can be good too for jumping back. But it's not good for most of the situations a person will find themselves in. In general a person doesn't want to have light footwork. They want to have fast footwork that isn't light. In fighting, if your footwork takes you too far away from your opponent then you will be at a disadvantage of always having to reset and trying to close the gap.
Outmaneuvering someone doesn't require light feet. That's a misconception that people make. Sometimes outmaneuvering someone is only a matter of inches. I will try to remember to record it, but I can show you fast movement to a target while in a horse stance. The gap will be a 6 inch gap. I will close that gap by shuffling forward a couple of inches. It will be fast movement with a heavy stance. It will be fast but only over a short distance. To avoid a punch one may only need to move just a few inches. It's the same for landing one.
This isn't a disagreement to what you are saying, I'm just highlighting that there is a difference between footwork that is fast and footwork that is light. Many times people think that you have to be "light on your feet" in order to be fast or quick and that's not true. When people speak of being fast or being quick, it should be put into the context of moving across a distance. The more distance that needs to be covered the lighter the footwork will need to be. If people keep that in mind, then they can determine how far to they need to move and then choose the correct footwork for it.