8-10k for 20-30 seconds on a Operation Boss?! Not a chance at all. Probably you get that number if you hit 5 targets with your orbital, but 100% not on a single target. With my sniper i parse about 3100 on dummy and i have a maximum of 4k-4,5k dps after 20-30 seconds.
I didn't have opportunity to experiment with pulling aggro on operations bosses but in FP's I can see that numbers if I pre-cast flyby and pop relic/adrenal. Then it starts dropping rapidly at stays at around 4k for a while. Probably on operation's boss it will be slightly lower due to resist chance. Maybe it's a bug but it's what torparse metter showed a few times.
Anyway my point is it is not really possible to pull aggro as ranged if tank knows what he is doing unless you try to do it on purpose.