If you work on your positioning a bit more, you’ll find that destro is able to free cast nearly all the time.
Destro is our strongest spec right now for bgs, with frankly overpowered killing potential. Pure affliction is pretty close, despite what the haters say, it does just fine rotting people.
Demo on the other hand, dramatically limits your output, for a survivability “gain” that is worse than just getting better at positioning.
I won’t link my channel here, but can search my name on YouTube for some examples on positioning. First 3 videos are 24-0 in my full pvp set, 11-2 wearing irradiated set (both deaths from being the last alive at lm vs 5+ trying to spin flag), and 16-0 wearing my full gnomer gear (and being sub 1500 hp unbuffed) in a game my team got stomped in.
I’ve also got a 31 affliction video I was debating on uploading (though probably won’t make many aff videos, the spec is strong in bgs, and fun to play, but a bit weak on the “excitement factor” for viewing purposes.)