I checked the logs and it wasn't you, but yes i do play on the bastion - which is where that video was taken from.
It is something that's available to them, but calling it "unfair" isn't being honest about the ramifications of the tactic. It's exploiting the terrain by placing an AOE above players, from a position is totally safe from any attacks, while preventing the attacking team from moving forward for an indefinite amount of time.
Unfair is accurate. I don't need to fluff up my adjectives to satisfy some quality threshold in your mind.
I believe it is an unintended aspect of the warzone. Much like jumping over the gap. Much like the double stealth. It brings in an element of clearly unintended unbalanced play and should be fixed. But that's different than an exploit.