So it had some use. But I still find it ridiculous that the only usefulness a new "skill" yields requires absurd amounts of micro management(which to be honest, probably isn't possible to execute). And, surely, this wasn't Blizzards intention. So... bleh.
But to clarify on the logic you are using, the determinant would be finding all the effective damage per rage values were of all abilities (after factoring in all possible increases such as battle trance and whatever else they added.) Whatever IR modified abilities yielded DPR rage values more efficient then rage dumps (HS and slam) would become abilities that you on/off IR for.
But again, this process is ridiculously meticulous and not worth the effort.