I don't get this denial of intelligence, to take it to a simple extreem, a smart Dino would easily beat a dumb one.Intelligence has nothing to do with big theropod fights, little theropod battles Intelligence may be something.
Carchorodontosaurus or Giganotosaurus were the king. T-rex is 3rd. First Giga and Carch are bigger and have the jaws strong enough(never mind bone crushing)to crush rexy's neck after two bites, if they're unlucky 3 bites. They're also more agile. The king is between those 2.
Oh, and by the way, Megalodon wasn't a dinosaur, we are talking dino king
T.Rex was a killing machine, an adult would have experience in hunting and outmaneuvering fish eaters.