Vanilla humans have always had the power to summon Outsiders. I believe that was the point in Blood Rites.
Free-willed humans, anyway. And, sure, the ritual to summon a champion like Behind worked OK with one low-level talent and two unpowered helpers, and maybe didn't strictly require Madge having been a weaker practitioner to pull off (although that probably helped get it done multiple times before making a fatal mistake). But the other methods that involve calling up a squad of individually weaker outsiders, like in CD, or DB / PG when the Reds were supported by mortal-summoned outsider foot soldiers, those do seem to need at least a low-level practitioner.
Even with the little fish being a lot more common than council-level talents, relatively few people want to sign on to unmake the world in the name of tentacled horrors from beyond. As Harry puts it, most people don't want to mess up the place where all their stuff is. But if you can upgrade a non-powered cultist who already has sufficient insanity, or empower some random victims who are too addicted to care about anything beyond more of the drug, that eliminates a bottleneck to bringing over actual armies.