Because its name is Quick sort, SO you cannot neglect constant, it will loose its property
and its not exactly O(n) it is cn c can be 10,100,1000,10000
as constant increase n will approach n2 Since recurrence relation does not accurately tell us constant required it is just an tool for analysis
T(n)= 2T(n/2)+Cn
no if N= 10000 and C=10000
then complexity will be O(n2) This is my approach any correction is welcomed