I practice Chen Style, and technically, there isn't a "correct height" to practice because it does vary due to things like one's age, health, or mood.
In theory, Yang Style was said to have different heights of practice, but whether or not the average person trains it that way is a different story. For example, Yang Banhou was said to have practiced underneath a high table, which forced him to practice low.
Low stance practice isn't really about usage, although it can be. Realistically, in usage, I will be in a higher, shorter stance.
The thing with low stance is to have the benefits of it carry over into the high stance. Because not only must I deal with my own weight, but I also have to deal with the additional weight of my opponent's pressure stacked on top of all that.
It is like training to lift 100 lbs to make lifting 50 lbs much easier.
Another incentive to avoid teaching a low stance is that it is less forgiving of errors. Any misalignment in the legs in the high stance is something people can get away with more easily. But once they get into a low stance, the consequences of those misalignments will be magnified.
So, given that most who practice Yang do so for health, I can see why they wouldn't want to teach low stance due to that risk.
Personally, I don't think it's about "Low stance" being more correct. Rather, I think it ought to be more like: "Does one practice low stance in addition to middle and high stance?" Because if one only practices high stance, they do not gain the benefits of low stances to carry over into the high stance.
There's also the question of: Does the methodology of their high stance still translate into the low stance without any compromises?
For example, there are a lot of "rules" that one holds in a high stance that they cannot figure out how to rectify in a low stance. For example, knee passing beyond the toeline.
Some schools teach "tuck the tailbone," where they push their pelvis far forward beyond neutral. As a consequence, low-stance practice will be more problematic for them because it will push their knees forward. Their knees do not have much room left in the low stance. It is by pulling the pelvis back that the knees can have more room.