I'm not saying the timeline didn't change, only it didn't change enough to be notable. They left a very small fingerprint. None of the butterflies were enough to be notable.But that doesn't answer my point about the butterfly effect.
If there was a timeline when the original Bell was Bell, and Sisko had to take over later and copy everything he did, the timeline would still have changed. Even if Sisko copied Bell's actions and words down to the letter, that alone would have caused a change. It didn't.
What about Trials and Tribulations? None of those characters were in the TOS episode, but now they are. As far as we can tell nothing changed in the 24th Century.