Which is true in real life, but i don't think it is necessarily true to airsoft so much. Range is mostly affected by FPS and hop up, barrel length is a minor factor.
Two guns with identical FPS, but different length barrels will mostly shoot the same ranges.
You do not need an 8" gun in CQB any more than you need an 14" gun in woodlands, I have ran my 18" Mk12 indoor cqb and its great, i have ran my 8" G5 outdoors and its great.
The size of the gun dictates your tactics, not its range, yes its easier with a short gun, but a carbine is also perfectly suitable for both indoors and outdoors.