Considering Preston's boss is like 5'7" and 140#'s, and also has a big input on the bike, I'd say that's not the issue. My take is Yamaha took a big step into uncharted waters with the reverse engine and mass centralization. While all the other bikes a virtual clones of each other. So they are the only ones pushing the development of this layout- which means it might take a bit of time to get it sorted before it surpasses layouts that have been being developed for decades now. Also- all the different manufactures have different durability and safety design parameters. Yamaha's probably being the highest. Look at the rear hub and brakes set up on a YZ and compare it to a CR- it looks overbuilt by comparison. But that is because that have set a higher failure standard their designers have to meet. This contributes to the bike being heavier than the others. Then mix in the thick ergo's, and you have a heavier felling bike. Lots to consider when building a consumer product, I'm a long time Yamaha fan, and own a current gen YZ and like it. I think its biggest problem isn't so much that it isn't good(talking chassis- the rest is amazing!), it's just that it's different. Like I said, all the other bikes are very similar than the YZ in design, and therefore feel. While the YZ is it's own animal and takes a bit of warming up too. But once you're there, it's a great bike.