Considering the quality of the island itself is a factor in Maldivian properties, based on my experience, I'd disagree with the assertion that Hilton/Marriott are winning in the country.
Between Conrad, St R, WA, and PH, I think PH takes the cake. The island of Hadahaa is truly special and spectacular, and its seclusion from the rest of the world gives it a solid edge, vs the larger properties Hilton/Marriott sport.
Obviously a Reef Villa at the W.A is peak for a standard redemption.
And we all have our personal preferences. I certainly would jump at the chance to visit both Conrad and W.A again- were my vacation days unlimited. That said, I will actively avoid Marriott, and in particular the St. Regis Maldives. (unfamiliar with Ritz, Alila, Hilton Amangiri, and J.W)