I'm trying to mount a TV into a brick wall covered by 2"-2.5" of drywall... is this doable?
I would bypass the drywall and long screws and flat mount 2x4 to the brick and then attach the TV mount to the studs with 1 1/2 wood screws.  You would cutaway enough drywall to achieve a flat mount.  You might have to add a 1x4 overtop to get the proper flush or slightly proud mounting.