Darius is at least a foot taller than Draven. Their official art proves it. Additionally, Darius is canonically bigger than Swain, and Sion is approximately 9-10 feet tall. If Sion is shorter than Darius it wouldn't make sense, since he's supposed to be this behemoth of a killing machine who can trample even the largest of men. Caitlyn cannot be taller than Udyr and Pantheon because they are both large-figured and imposing figures that strike fear in the midst of battles. Udyr has gone toe-to-toe with bears and beaten them, so naturally he would need the height closer to a bear than shorter than a scrawny (sorry, she doesn't seem like the type to be lifting weights being a sniper) marksman. Additionally, Aatrox is also an imposing figure, towering above the heads of regular men, his sword matching the height of the largest soldiers. He wouldn't be as inspiring if he was a tiny dwarf man screaming around telling dudes to follow him. People would take him as seriously as Milhouse Manastorm. I'm guessing he is around 8'3, and if that's a stretch maybe 7'8.