I am a yamaha fan, and a lot of people are pointing to the bike for the bubba's recent below his norm. performance.
and I really don't think its the bikes fault, at least not in the way people are thinking (as in the bike suffering from poor frame geometry, over heating shocks/horrid shocks) or poor ergo's. I think its something a long the lines of why Reed didn't do that hot the year he rode the kawasaki. Riders and bikes need to gel together, just because one rider does horrible on a bike doesn't make the bike horrible, I mean, DM18 did just ride the yz450f to his best SX season ever. What I feel it likely is, is just a matter of Bubba can't adapt to the yz, like Reed couldn't adapt to the 10 kx450f. Will he do better on the suzuki? It's likely, the rmz is a bit closer to what he's been riding for years, the yz is a fairly new design (I'm aware that reverse slanted cylinders have been tried in the past, none with any success) and it does handle a tad different, even a rider of my skill level can tell you that, it feels a bit different than the others, but its still very competitive.
Reed managed to make a switch that saved his career. We'll see if Stewart can do the same.