I would be hesitant to tie the ability to purchase refinement exclusively to an effect granting a bonus on knowledge, but I wouldn't see a problem with that being one option among possibly several others.
I would suggest such a quasi-stunt follow a pattern similar to Occultist (a bonus which grows as the question draws closer to the character's specialty).
ex:
Joe the Pyromancer
Channeling (Fire) [-2]
[Skilled Focused Practitioner] [-1] (+1 bonus to Lore on research related to evocation effects, with an additional +1 bonus if that research focuses on effects associated with the element of fire; further, Joe may purchase refinement for the purposes of specialization applied to Channeling-fire)
Refinement [-1] (+1 power and control for evocation with the element of fire)
Alternately, we could replace the 'stunt' with a half-refinement/half-stunt, which would also solve the issue of the pyramid and whether refinement choices can be split.
ex.
Joe the Pyromancer
Channeling (Fire) [-2] (+2 control, +1 power)
[Skilled Focused Practitioner] [-1] (+1 bonus to Lore on research related to [element//functional/thematic group] and +1 power, complexity, or control with [element//functional/thematic group])
Refinement [-1] (+1 power and control for evocation with the element of fire)
Nope. It's charging 2 refresh to break the requirement for following a ladder / pyramid. The higher you are on that pyramid, the more it's worth.
And here's where we differ. I don't see it accomplishing that as written.
To short circuit the argument, though, let's give you the benefit of the doubt that
this incarnation of the power is broken in that way (which, if it were, would indeed be powerful).
Let us then envision an otherwise identical power which did not suffer from the same problem (ie. did not obviate the need to follow the pyramid). How would you price that power?