The WSM will also kick slightly less than it's larger cousin
That does apply only in rifles of the same weight.The wsm isusually chambered in lighter rifles than the 300winmag and since rifle weight is one of the most important factors in recoil,the result is that most ofthe wsm rifles provide as much recoil as the 300winmag rifles.
Shorter and fatter cases are inherantly more accurate than longer skinnier cases.
A short action rifle is inherantly more accurate than a longer action. It is more rigid than a longer action thus flexing less when firing and under recoil.
Theoretically this is thought to be correct.However the quality of the rifles and load are far larger factors in determining accuracy than the cartridge.In the case of a custom target rifle and match bullets you may see abarely measurabledifference in accuracy,but it certainly will not be noticeable in a hunting rifle using hunting bullets.