How to set things right.
1. Make FR baseline.
2. In its place on the talent bar, add Heroic Strike as an off CD rage dump that replaces FR.
3. Remove slam rage cost.
Arms needs a rage dump, that itself is a flaw in design. Slam doesn't cut it since it's on the GCD and is competing to much with other skills, it should be a 0 rage filler. FR fits to many slots on its own since its something the spec flat out needs. So just make FR baseline, but give us Heroic Strike as an option for people who do not care for FR playstyle.
There, spec fixed. No more down time. A rage dump for everyone. Maybe buff Overpower so its useable.