Seldon's psycohistory predicted the path of the whole empire with great accuracy, but knowing their destiny would make people act differently, so Terminus didn't have psycohistorians, just a vault that would open at crucial events and give information. It would have worked well until the Mule threw a wrench with its mental ability to tune other minds. He wasn't a clairvoyant, he just altered people's feelings. The Second Foundation put the plan back on track thanks to their own mental abilities, but they also weren't clairvoyants. So far only psychohistory could predict the future. Later we have Golan Trevize, who also couldn't see the future, but had a gift for choosing right with incomplete information. Even Gaia had to rely on Trevize for its final decision.
Foundation's Gaal can see the future, and this is a world breaking ability. Hari Seldon and his psycohistory become obsolete since she can do that on her own, any action against the Foundation is moot, any deviation from the plan can be predicted, etc.
The only way to write Gaal out of that corner is making her clairvoyance work as reliable or unreliable as the plot needs (lazy writing), and judging from how she can predict and block micrometeorites now (which can puncture a ship's shield and hull, but not a tablet), it seems that's the route they will take. There was no need to introduce clairvoyance in the Foundation's universe.
