Without Taylor Hebert, the odds of humanity surviving the Entities plummets.
Noone else could have beaten Scion, at the least not in the way she did.
I don't think the point of divergence will be something like preventing the solution to Gold Morning. Changing it, maybe, but the date's all wrong for that.
At a glance, the most pertinent phenomenon
specific to Brockton Bay circa 2011 were Labyrinth, Bakuda, Panacea, and Echidna.
Labyrinth is sort of in a weird spot here; it's more that she could facilitate other civilization-ending threats than be one herself. Just ending Earth Bet probably wouldn't be a Singularity except insofar as the Warrior would still be around, which wouldn't be a victory for their enemy. So it's got to either derail history for every other world, or somehow have Brockton Bay problems show up in 1780. In the first case Labyrinth is the most obvious suspect.
Bakuda, as a natural trigger, is a case of "couldn't destroy the multiverse under normal circumstances but might manage to do something funky with the right power interaction and access to a Holy Grail and/or heroic spirit shenanigans."
Panacea is a similar case. Plagues aside I think she could merge all humans into a horrible flesh tree. Sort of an early End-State Cycle. Bonesaw would be green with envy. And chlorophyll.
All bets are off regarding the Echidna Event. Zero effort was put into making her power safe for distribution in the Cycle, and she ends up cloning Eidolon who is even worse. Could they blow up the multiverse? I dunno. I certainly think if Ignis Fatuus learned how to vampire other people's Shards to refuel his own powers back to Eidolon's maximum there's not a whole lot most people would be able to do about it. He went down to Miss Militia's Neutral Special in canon though so who knows. Echidna could also clone Labyrinth or Panacea so, that would be fun.
And of course any of this nonsense could show up in early America and no-diff the Founding Fathers, the good-for-nothings. But so could most of the stuff on Earth Bet, so Brockton Bay isn't special there.