I think that it really depends on the map and how you engage. The Red Death is currently the darling of the Crucible because of the healing factor, but that really only applies to med/med-long engagements. Rusted Lands and Shores of Time both have good long sight lines that can lend themselves to scout rifles in general. Twilight Gap and Blind Watch also have several avenues that can be abused by someone with a long-ranged weapon. But in order to fully exploit the Scout Rifle's strengths you are subjecting yourself to a particular, sit-back play style. It is true that on those maps you are going to be competing against pulse rifles, and steady-handed Thorn wielders, but scout rifles will have every other gun out ranged, it just comes down to tapping heads. The real issue right now is that there aren't more maps for those who like to run scout rifles to play on. But next time combined arms comes around give that playlist a go and see how you fair on larger maps.