If the starter system is working right, and the motor has an issue with the auto-decomp system, the starter just won't crank the motor fast enough, and may even stop on the compression stroke. So that's not your problem.
If the starter whines but doesn't turn the motor, something's slipping. Broken teeth on the starter gears, or bad one-way clutch. It only takes about 10 minutes to get that clutch cover off and find out.