AMEX Platinum is not about points, but benefits and status. AMEX Platinum does not give you upgrade unless you book through FHR, a program special for AMEX Platinum and Centurion cardmembers.
If you are point-savvy, AMEX Platinum is not for you. In fact, a lot of AMEX Platinum cardmembers also have AMEX PRG with them.
So in your case, what important is to identify the brands that you will have a relationship with, and apply for the affiliated cards.