The Grizzly 700 won this shootout because it had the best combination of handling, steering, suspension, and power. Power was likely the lowest contributor to the win, because all the others were faster, except the Rincon. But there was enough power, even with it being on the lower end of the spectrum. So that means suspension, steering, and handling are what make the Grizzly 700 "best". Everything I read gives credit for the Grizzlys performance in these areas to the power steering. But there is more to it than just power steering. The power steering is largely transparent when you are riding the Grizzly, except for when you hit something with one front tire that would normally jerk the handlebars to the side, and except when you have the front differential locked. Other than those times you really don't feel the power steering, even though you know it is there working for you. The other changes Yamaha made to the Grizzly 700 also contribute to its great handling, and its responsiveness to rider input, but those changes are only briefly mentioned, or not mentioned at all.
Yamaha made a concentrated effort to centralize mass on the Grizzly 700. Heavy items were moved down, and to the center of the chassis. The differentials were moved toward the middle of the ATV, and the a-arms were angled away from the center to acheive the same wheelbase. The gas tank, with the 50 lbs of gas it holds is now located smack dab in the middle of the ATV. Take you seat off and look at where the gas tank is, there isn't a better place on the ATV to put that 50 lbs of gasoline. The shocks were moved from the upper a-arms to the lower a-arms. The engine was lowered in the chassis, and rotated forward more to lower its mass. I suspect that all of these changes have made as much of an improvement in handling and manueverability, or more of an improvement, than the power steering did.
Mass centralization is something that has been the buzz word in dirt bikes for many years now. Honda claims that they came out with the dual exhaust on their CR 250F to improve mass centralization, not because of an increase in power or decrease in noise. Yamaha just redesigned their exhaust silencers, and changed from the usual perforated core style to a much shorter mechanical baffle style silencer, which they also claim was for mass centralization. To understand what mass centralization does to an object, take a 6 foot long barbell and put a 20 lb weight at each end. Grasp the bar in the middle with both hands being about six inches apart. Now rotate the bar clockwise by 90 degrees, then counter clockwise by 180 degrees, then clockwise again by 180 degrees, and just keep doing that until you get a good gauge of how much work is involed in doing it. Then take those same 20 lb weights and move them to the very center of the barbell. Grasp the bar in the same place with your hands, and repeat the clockwise, counter clockwise rotation proceedure several more times to gauge how much effort is needed. You will notice that is dramatically easier to manuever the barbell with the mass centralized. The same priniciple applies with motorcycles and ATVs. With motorcycles they are down to moving mere ounces of weight each year in an effort to centralize mass. But with ATVs like the Grizzly they had alot of weight that could be moved. Shocks are heavy. Differential gears are heavy. And the 50 lbs of gas in the gas tank is real heavy. So there was greater improvement with the Grizzly 700, relative to the old Grizzly 660.
What this has done is created a Grizzly that responds much easier and much faster to rider input. It feels lighter and easier to ride, even though it weighs the same. And the power steering doesn't hurt either.