There's a lot of game-ism in how some Minor/Major magical Focuses get determined. My general guideline to to be more generous for major focuses than for minor ones, as a minor focus I view as more of a character 'accent', whereas a major focus is true core concept, especially as it takes your one major hermetic quality slot.
For example, I'd allow a minor magical focus in 'ghosts' or 'airy spirits' but not 'magical spirits' - there are multiple canon PCs with ghosts as a focus for example, so it'd be a little much to allow a strictly broader classification and still have it function as a minor magical focus. On the other hand, with a major magical focus in spirits I'd allow to not only encompass 'magical spirits', but naturally incorporeal fae - Faerie Jinn, for example - and most demons and angels as well. (Angels/devils/demons are described as 'nothing but souls' in ArM 5 core, I am not responsible for resulting angry Quaesitorial axe-squads or angry archangels or demonic princes should the magus attempt to actually use this aspect of the focus to mess with God/Demons, Arcane Limits still apply, etc.)
Philipus Niger's "dispelling" (minor) focus seems to apply to a wide variety of might-strippers across Realms per his statblock, which to me, felt a bit generous, but that could just be an issue with how I conceptualize the might-strippers. I'd totally give him it for Wind of Mundane Silence, The Heathen Witch Reborn, Shattering the Malicious Rune, which it seems perfectly aimed at, but I question whether stripping the might from magical creatures is 'dispelling' them. Still, it clearly seems intended, so I'll roll with it.
So to me, a Major Magical Focus that encompasses counterspelling would fully include the domain of dispelling, but also include spells like Mirror of Opposition, Supressing the Wizard's Handiwork which alter magic to bypass or change it against its original intent, rather than trying to destroy it. The subtle 'big one' here for 'counterspelling' as a Major Magical Focus is that it IMHO also generally includes any fast-cast spell defenses against magic. Which is pretty neat since it helps for really any TeFo.