Whys that?
He sold more albums than both of them combined. (Two times their combined album sales in fact - Prince 150m, Bowie 100m, Jackson 500m).
Thats not the only metric of course, should we go with popularity? How his music has stood the test of time?
His talent as a performer?
By almost every objective metric you can think of, Jackson beats Prince and Bowie.
All you have is, you prefer Prince subjectively, which is fine. There are other artsists I prefer over MJ (Freddie Mercury is the GOAT for me, but that is subjective)
The only thing I would give you is Prince will certainly out do him when it comes to writing hits, if we are going by pure numbers as Prince was prolific as **** with his writing, not just for himself, but other artists.