There are plenty of character concepts that give both Speed and spellcasting. If this Power benefits from Speed, then all of those characters would be well advised to take it.
That would be bad, because casting with Athletics is weird and should not be common.
Also people with Speed and Evocation really don't need a buff.
So Alternate Magic Paradigm should not work with Speed.
Not sure why Strength is a worry...Strength doesn't directly boost Might.
Anyway, here's an edit:
ALTERNATE MAGICAL PARADIGM [-1]
Description: Your magic is different from everyone else's. Where most practitioners cast spells with mental strength and magical knowledge, you use other methods.
Musts: You must possess at least one spellcasting power in order to take this one.
Skills Affected: Any three.
Effects:
Alternate Magical Paradigm. Pick three skills. For the purposes of any spellcasting Powers you possess, use the first in place of your Conviction, the second in place of your Discipline, and the third in place of your Lore.
No Shenanigans. If any of your Powers or Stunts provide a bonus to one of the skills you picked, that bonus does not apply to your spellcasting.
Does that look okay to everyone?
I tried to word it so that spellcasting control and power bonuses would clearly be unaffected. Let me know if I failed.