I've noticed that a lot of RWGPS routes aren't actually proper routes, they're just waypoints. Devices with built-in waypoint navigation will consequently build their own route between the two points of a track so you don't follow the route as planned. I've had the same problems using a Mio (Cyclo 505) device so it's not particular to Garmin (both my 820 and 1030 plus do this), this is no problem on older devices which follow a breadcrumb type trail or just have an indicative path, but for devices which have a proper navigation function it's problematic.
The Wahoo devices generally (with a particular exception) dont' do on device re-routing and navigation so don't fall foul of this, and I think the Wahoo integration with RWGPS is better done so the planned route is used exactly. When transfering to different devices you're at the mercy of how the device interprets the generated route. For this reason I don't use RWGPS, it doesn't build usable routes when exported.
The best route builder I've found overall is the Strava route builder, it builds excellent routes that work perfectly with devices that have on-unit navigation (Cyclo 505, Edge 820/1030+), I've tried others as well as software on the computer to build routes, but none really work quite as well. Garmin's route building software is OK and produces good files, but the interface isn't as good to use as the one Strava have built.