yeah well.. no..
demo was good so far that you had CONTROLLED movement and you had to move seldomly..
As soon as you started moving a lot, damage for demo plummeted..
hence a LOT of NH mythic encounters were REALLY shitty for demo..
and that's when a lot of people just said "bye bye" to demo, because affliction got supercharged in parallel..
demo in bfa so far looks the same immovable stick..
what can you cast while moving? you have no dots, and your generators needs to be hardcasted, same for your spender, and your "proc"[core] depends on both spender and consumer to actually get some core..
so yeah for normal and maybe hc it will be fine.. but where you will need execution and flexibility you just won't raid as demo, unless your damage warrants the raid leader cutting you some slack about moving around to do mechanics..
it's such a pity..
for me pandaria SoT demo was very good, just like WoD foundry lock was also incredible both gameplay wise (damage, possibility to burst, cleave potential, and movement via demonic leap) and lore wise (you meddled so much with demons that you became capable of wielding demonic-like aspect)..
legion demonology fit the lore as a imp massive summoner, but the clunkiness of the roation made it problematic along with lack of movement option, lest there were two+ targets and you could spam demonwrath while moving..
bfa demonology so far seems even worse of, with forgettable damage, though lore wise it's even more fitting than legion as a demon commander rather than an imp spammer..
time will tell, but so far, i'm less than impressed