There should under no circumstance, other than a deliberate exemption, be a situation in which skills that vary in overall power are allowed to cost the same amount of Memory to use.

If for no other reason, then simply because a single point of Memory available, should have a consistent value in terms of power the player is allowed to exert.

I have suggested a superior alternative(skill points add school-specific Memory slots), achieving a similar goal in a much more organic way: by operating on the player's capacity(which is how Memory gains work already) rather than adding another vector for multiplicative scaling.