I think a lot of this is in issue really due to the power levels and the concept this create
I see it as you can do a Focused Practitioner feet in the water, a sorcerer at Up to your waist, and a full wizard only at chest deep.
The sorcerer not being able to take refinement makes total sense, they is a CLEAR difference between sorcerer and wizard in ability, which is represented by refinement, and they they are often not born wizards, and thus lack the sight and the constitution sometimes.
The issue I see is more with focused practitioners, which is described more as an innate talent with a particular element or thamaturgic area. If you want to play just a pyromancer or just a ward specialist and not deal with other elements or thaumaturgy, then doing so at high level, without the ability to refine your one element, or wards, or whatever, you do top out and can't go far.
This does NOT fit with harry's description of them being "specialist" not generalist, and that they can be VERY powerful in their chosen area, (see YS 76), or binder if he doesn't use focus items. So for them to fit this description, the lack of being able to increase their command of their element through refinement does not make a lot of sense in my mind.
Now, perhaps making refinement only add 1 to their element makes sense, or apply refinement normally, or an Idea i just thought of, what if refinement could also add just to a ROTE spell, to control or power individually, rather then globally, so that it has to be more spread out, and that would make it feasibly possible to still use the support structure
I am not arguing with anything anyone has said, I am just curious if people would agree that this is where the issue is mostly coming from? (and curious what people think of the idea that just occurred to me while i was writing this)