The new four strokes are lighter, do handle better than ever before and offer compression braking over the 2-smoke. With enough torque most 4 stroke race bikes only run with three gears and only shift between second and third. On a tight course they seldom need to shift gears at all. Just roll on the power.
The reason racers are moving to four strokes is the law. A few years back California was the first state to ban all two-stroke operation of off-road bikes on anything but a closed course. This is what started the sudden development of a competitive four stroke race bike. If you want to race in the future it will be on a thumper. It's only a matter of time before two strokes will be banned in other states as well. Then the 2-cycle weed eater, chain saw, leaf blower and such will be next.
The EPA is trying to put the squeeze on small engine manufactures such as Briggs and Stratton to catalyze and lean the small four stroke engines. They are resisting stating the change as much too costly. I am sure the little engines pollute but when you consider the minimum fuel burn per year I think they can find much bigger pollution offenders to clean house with.