I think your approach is exactly right, OP! There are always reasons to relax some rules, in certain circumstances, but as you have explained this situation doesn’t fit.
I will say that there aren’t really any industry standards for lessons and showing, but I think most programs try to structure things so their horses and riders are successful. It’s really going to depend on a lot of different factors. For example, when I was a junior I always had green horses. When we first got them the norm was one training ride for the horse and one lesson for me, with flatwork the rest of the week, until the horse was sufficiently far enough along that we could dispense with the weekly training ride. At that point, whichever trainer was doing the green division on my horse would school it as necessary before a show, along with one pre-show lesson for me. For other juniors, who had made hunters, jumpers, eq. horses, the norm was something different, as it was for the ammies.
Right now I train with eventers but I generally do one lesson a week (which is part of our boarding agreement), and certainly do one before a show. Other people have a combination of training rides or extra lessons; because they are all eventers there is a lot of just (dressage) flatwork that is done every week along with the jumping. Sometimes my trainer will do a flatwork session on my jumper to install a new button or polish one I’ve been having trouble with, and so on. It’s all conditional on what is needed.
I was at a barn for a while that had two different trainers, and everyone who rode with the one who only taught kids never rode their horses or ponies outside of lessons. That was a little crazy to me, especially since the “lessons” were often more just meandering around and chatting than getting any actual work done. But, it seemed to be acceptable to those people!