Lemme hit you with some little known facts about T.rex and other mega theropods.
They all average out somewhere at the 12-13 meter range. Giga and other charcharadontids tended to be slightly longer than the king yes, but T.rex was slightly taller, having longer, more muscular legs. And far, far wider. T.rex is like a quarter to a third wider than any other mega theropod.
So you see, the other mega theropods only actually beat T.rex in one dimension. The problem here of course is that we live in a 3 dimensional world, and ol' rexy beats 'em in all the others.
The exception to this of course, is the Spinosaurus. Who's height is deceptive thanks to its enormous sail, was a very thin and elongated animal, and it had denser bones to help with buoyancy, much like a hippo. But in mega theropod comparisons Spino is kind off the odd one out, he's semi-aquatic, and therefore cheating, because it sure is easy to grow big when you have water to help carry your bulk around.
tldr; T.rex is still king baby, it was never dethroned.