The flow is fine. I got out of freshwater tanks for a while and just had my saltwater setups. When I got back into freshwater I had the same question as you. I have been running heavy flow on all my freshwater tanks and it doesn't seem like my fish don't mind at all. Pickerel which people claim can't live in a tank with fast current, hangs out directly in front of my Jabeo wp40 at full blast.
Rivers have a good amount of flow in the wild, even ones considered slow moving. The Oscars behavior should tell you if it is to much flow.