I used this to get exalted with WSG rep on my DH. Let me explain how it works from first-hand experience.

All your gear scales down to a certain ilvl but all procs & enchants deactivate. The only procs that work are heirlooms. When I was doing it I used the WoD demon shield loom and battlemaster's trinket. Food buffs get scaled down, this is very good with legion food. I normally used fighter chow for a passive heal out of combat. I also had my friend heal me while I took the flag. From my experience, though the whole horde team would get distracted in mid allowing me to be in tank spec and just leap to the horde flag room.

It's not really an issue of scaling, it's more an issue with lower-level characters not knowing how to deal with DKs or DHs. They're very killable if you know what you're doing. The only thing that makes it kinda OP is with fighter chow or other legion food buffs.