Someone with any form of spellcasting that included focus slots can create potions, and those potions can do [mumble, mumble-mumble]. Er, the book isn't clear as to what limitations are imposed on people who have less than full wizard abilities (Evocation and Thaumaturgy) but who have slots. Some people think focus item slots are focus item slots are focus item slots. Others think that focus item slots can only be filled with items that reflect the caster's powers. So can a character with only Channeling (Fire) -- which includes 2 focus item slots -- use those slots to own a Dresdenesque protective duster? The RAW doesn't say no, which is typically interpreted as a yes.
But back to your question, which I think was "can a potion slot be used for an 'offensive' spell?" If you look at the sample "potion" list on YS303+, you'll see several examples of just that -- "potions" that generate attacks -- and aren't necessarily actual potions at all. For example, Ghost Dust and Sunburst in a Hankerchief.