Having similar issues with a 2012. Rear brake wouldn't hold the bike on a parking ramp unless I really pressed on it. Slow speed maneuvers were not comfortable because rear brake was weak.
After 1000 miles I started to notice some improvement, but still not what it should be. The service manager is waiting for a response from H-D. They have had several new RG owners with similar concerns, haven't seen it in the other Touring bikes.
The first service they bled the system twice with no change and the second time in the shop they bled it twice with some improvement.
Not holding my breath on a quick response or fix.
12 Road Glide Custom