In making it a pure "merit" role, you then limit people who don't have the resources to compete to get these roles, especially if major actors are vying for it (of which only few actually are in the LGBT community). As such, not seeking out LGBT actors for these roles serves as gatekeeping, where LGBT can't get these big roles because they don't get these big roles.
How is that gate keeping? Having open doors for actors to audition is not gatekeeping. If they aren't getting roles because they aren't big names, then maybe they should start small and built up practice working in a professional environment, flexing their range of voice and acting.
Actively seeking out people to fill a quota and ignoring the creative and professional process is in fact gatekeeping.