Yeah, that bugged me with the Titan sized combiners.Why? Wouldn't it make sense to make him in-scale with the other combiners? Fictionally-speaking, he's not supposed to be bigger than his peers.
Heck, even his original toy was the same height as the Scramble City-type combiners. It was only Predaking who towered over them all, and he wasn't dramatically bigger than the other combiners in the fiction either.
Especially when we got Volcanicus. Hey, the Dinobots can combine now, and take on Predaking on even footing! Just like in the cartoon based on the line, even!
*Titan class Predaking comes lumbering in, towering over Volcanicus*
...never mind.