As for white sharks vs dolphins, I think it's probably similar to cougars vs grey wolves. White Sharks prey on individual dolphins on occasion. It's not really a contest one on one. But dolphins travel in pods, while White Sharks are loners. Same thing with couger vs wolf. An adult cougar would stomp all over an individual wolf, but wolves travel in packs. A cougar that sees a single wolf knows there are most likely more hanging around somewhere, so it leaves before trouble starts.