Ambus is about the size of the recent Targetmasters guys that came with the Legends figures, maybe a tad smaller, and if he really was Legends size, he'd basically BE the cab, not sit inside it. Not sure why he was refered to as Legends rather than Minicon size, but then Americans have never really mastered the English language

I get what you mean about UM not really being all that solid, but he's on par with Jetfire and Megs, the only other Leader class moulds in the Generations line, and as Gok said, MP is a whole other league.
(I still prefer the CW Magnus aesthetics though, might just be my preference for the IDW designs)