This paragraph says it all:
You’ll be reloading frequently, with no buff to how fast you can do this short of using Flared Magwell or Pulse Rifle Reload Gloves. Even with Flared Magwell, now you have not-so-great Stability, and the low Magazine Size of 24 to contend with. The slow RoF is a big enough penalty that even with your relatively hard Impact, you’ll do less DPS than the faster-firing alternatives that you could roll with more PvE-friendly perks. Really, the only way we’d recommend using The Messenger in generic PvE content is with a Solar or Void Adept specialization.
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But at one clip with no reload the messenger does more damage. I would rather kill things without reloading at all. And when you are engaging bosses you will have to take cover constantly, being able to dish out more damage without reloading at all is better. Just reload at the same time your health is regening while hiding behind a rock.