re: I read that, but...
The problem is we have abundant geomorphological evidence there was abundant liquid water with huge running rivers and lakes on Mars early in its history. Some of these predate the origin of Meridiani or at least the currently exposed surface.
I also doubt their conclusion that the conditions at Meridiani are uniform across the planet. The orbital spectrometer observations show wide variations in the amounts of sulfates and clays, and various combinations of them, and in their estimated dates of deposition.
Robert Clark