I will say the cult didn't help the situation any, no, but the events of Persona 3 were largely unaffected by Strega's activity. Their existance had little to no impact on the events relating to Nyx and the Dark Hour.
Now I get to go into just why they were so awesome.
P3 had a very intangable force the characters were fighting against. It wasn't something with a plot, there were no intricacies to Nyx's plan, only it's coming. Strega, and Takaya most of all, was something P3 using as an antagonist. Takaya symbolized all of the reasons why Nyx was coming, and he embodied that role perfectly. He was a manifestation of what the players were fighting against, and something that would force them to realize the situation and move forward accordingly.
However he had nothing to do with whats happening now. Look at your own statement, the world now is as it was before P3.
It was years before P3 all of this started happening. The world a few years prior to P3 didn't see Strega in action, so we can safely assume they weren't the cause of anything. This shows Strega's utter irrelavance in terms of the state of the worl, regardless of their importance in P3's story.
(I feel that a character like Takaya is what Square enix intended Symore to be, only they failed horribly.

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