If time is an issue adding weights might be a good idea. I wish I had weighted down the bag for the ESB I sent to the NHC. I didn’t leave myself quite enough time to get that one done and having the hops immediately sink into the beer would have helped with the aroma I think.
Otherwise, I agree. Given enough time they’ll sink on their own.
I either put them in a nylon bag, or just toss them in (leaf only!) but use a surescreen on the dip tube.
I toss in pellets and bag leaf hops in muslin since they are cheap and I can just toss them when done.
I have seen the hop bags float! I don’t use them anymore, but sure enough I have seen them at the top of the keg. Just because, when you finish the keg and pop the lid and the hop bag is at the bottom doesn;t mean it was there the whole time. 
I weigh them for the same reason. Plus, I want to get that aroma infused into my beer as soon as possible. Since the beer at the bottom gets pulled from a keg first, that’s where I want those hops to be!
Every second counts man. Get those hops in full contact for as long as possible. Haven’t had an IPA in awhile… hand starting to itch… gotta…get…some.