If anything, Donnie's latest movie, Prosecutor, is a validation that he deserved more of the lead role.
Simu is a good actor, but i would rather bet my money on Donnie. Yes Simu is younger, but Donnie can still fight and choreograph the scene too. For every stuntman swapping actions Donnie does not do, Simu would not be able to do everything by himself as well.
What concerns me is, why it took the producer so long just to inform Donnie? If you do not want him to be Wei Shen, tell him in his face, and do not play the long game. Just basic manner.