Naturally speedy characters will try to move around you quite a bit, running, jumping, dodging honestly the easiest thing to do is while firing move close to them little by little and then right when you are in range melee. If they start running when they get low do not and I repeat do not follow them especially if they are connected to the voice chat because they could be sending you straight up into a deathtrap. You also want to corner them to a point where it's hard for them to move around and hard to dodge. You could also adopt the sweet business w/ actium war rig setup I personally (while I have not tried it on my acc) think its pretty well used especially when attacking speedy characters. If you don't like considering any of these options you could always adopt something like Antiope-D or New City for short range and primary (I don't recommend New City because of it's crazy recoil) and Uriel's Gift, Prosecutor, or Positive Outlook for avg range. I run warlock most of the time so these options naturally work well for me and same thing with a couple of my friends enjoy these types of setups as well. I personally run Origin Story w/ Last Hope on my warlock last hope for short range and Origin Story for long range. Sidearms like last hope, Eulogy S14, or the last dance will work well close range but fast characters naturally get out of those situations quickly (unless you corner them). Most Auto Rifles and Hand Cannons will destroy them at medium to long range. I personally use Crimson, Better Devils, or True Prophecy when using hand cannons and my Autos are normally Valakadyn, Origin Story, Positive Outlook, Prosecutor, or Uriel's Gift. These are all things I do to go against fast and resilient players and they work for me (Well the titan one I have only used 4 times and that was on my friend's acc) hope these suggestions help =) (srry for lack of punctuation, hard to make posts like this w/ punctuation).

Your description leads to believe you're engaging in the mid distance range spectrum, and if that's the case I'm guessing a fair amount of meta AR usage. I'm a Hunter, and the way I combat this is to close distance and deploy 2 CQ weapons almost always. Flinch is less of a factor there.....but also greater risk/reward. It's an approach trade off and requires reworking your tactics for those occasions when you throttle up aggression and/or adjust how you defend.

Go vertical