While I'm all thrilled at the idea of "free" extra dice for the other 4 categories. I'm thinking your selectively ignoring the first 2 times it states by spell type for the one time it doesn't.
1. SPELL FOCI
Spell foci empower Sorcery skills. Each spell focus is
attuned to one of the five category of spells or rituals
(Combat, Detection, Illusion, Healing, and Manipulation)
when it is created and cannot be changed.
2. Counterspelling: Counterspelling foci add dice equal
to their Force to any Counterspelling attempt, as long as
the countered spell is in the same category as the focus.
It also adds its Force to your spell defense pool.
So, we have Spell Foci telling us that each foci is only for 1 category of spells.
We also have it telling us that it adds dice to Counterspelling attempts, also if its for the same category. Please note it says Counterspelling.
Not Dispelling. So by that statement alone the part about Spell Defense Pool shouldn't even be in there as Counterspelling covers ALL uses of the skill, Dispelling & Defense. Now if it had read Dispelling & was only talking about 1/2 the use of the Skill then maybe I could see your reading of it.
But all I'm seeing is that its not repeating, for what would be the
3rd time in 2 paragraphs. That would seem excessive wouldn't it?
That they writers didn't repeat themselves 3x in a row doesn't seem, to me, that what they intended to do was break the rule for all spell foci by allow it to apply outside the basic parameters of limited to Spell Type.