Taurox's are taller, but not as long as Chimera's. And comparing the size of the models. The Taurox is half cockpit and half troop carrying. So, granted the Taurox's carrying bay is taller than a Valkyries, it is definitely not as long. And as for weight, the Sky Talon Varient (One that replaces the canopy with a crane) can carry a Leman Russ into combat without sacrificing it's maneuverability. That's, canonically, 60 ton of tank. I refuse to believe that 12 guys weigh 60 tons... In order for that, they would have to weigh 5 tons each. And if we assume that the Canopy that houses them is 10 tons of that weight (Just for arguments sake) then that would still mean that each guy would have to average 4 tonnes each, just to have same weight. My Minotaur probably, more or less, weighs about 3/4 of a ton... A Terminator might weigh 1 or 1.5...

So, when you do the math, weight is not an issue.