In pvp as a Arsenal i feel quite mobile, i move alot, i use explosive dart alot and other insta cast missiles, rapid shots HSM, Rail etc get in a good spot and do rotation from there.
then move, think of irl artilery, cast move cast move.
This sound like Pyro, i know but i dont like pyro and when you have the rhigt timing w arsenal, opponents will go down fast! Faster compered to anny other class i can think of, its what i love w Arsenal.