The entire point of the patent license is that they can't sue you for violating any patents that cover the library you're using. So it's at least a bit over-broad to it puts all the power in their hands.
The problem with the patent clause was that it prevented you from suing Facebook for any patent infringement, even if it's unrelated to React. If you're a React using-company, this more or less meant that Facebook had carte blanche to infringe on any your patents at will in an exchange for a license to use their React patents. That's a quite one-sided deal.
