Wall of text incoming.
So I'm going to preface this by saying that this is from a realistic and technical point of view.
When asking to balance Destiny weapons separately for PvP and PvE, you effectively double all of the workload for everything in both modes. It's not like the changes are copy and pasted over to PvE when PvP changes are made in the current architecture, it's the same gun being edited and the changes are effecting everything. This keeps guns feeling semi-consistent across both modes.
So When asking for separate changes, Bungie effectively has to have two independent environments for weapons, containing the thousands of guns available in game. Adding a new gun is now twice the work as it has to have a PvP version and a PvE version, new perks are now also twice the work to create and to tweak. This will effectively double the time it takes to get balancing patches out because guns that are "overpowered" in PvP will now also need to be tested and tweaked independently in PvE environments, and changed effectively and vice versa.
Now all of you may be saying "Yeah! That's exactly what I want!" but you fail to realize something. This may work out fine at first, but once the two branches of balancing diverge from enough balance patches, a few scenarios may happen.
The guns no longer work anywhere close to the same as they do in the other environment. It would be extremely hard to make both guns feel like they are the same gun when they are being managed by two separate teams. A company of Bungie's scale and a game of the scale of Destiny (and assuming that D2 will be even larger and more complex) will struggle coordinating teams, fixes, tweaks etc. Imagine if PvP gun A got a nerf to range but PvE gun A did not. Now PvE gun A got a buff to stability but a nerf to impact and PvP gun A did not. Inevitably people will start crying on the forums and Reddit saying things like:
"Why is it that hits like a damn truck in PvP but shoots cotton feathers in PvE? WTF BUNGIE?!?!"
filthy casual concerned Guardian.
Weapons stay close to the same but patches, fixes, updates, etc all take wwaayy longer than they currently do. This would happen because to coordinate between the teams and make sure everything is fine between both environments would take a huge amount of time. Imagine waiting 8 months for balance patch 1, and 5 months for hotfix 1.
And that's just off the top of my head. On top of the above, moving between PvP and PvE would take even longer than now, plus there may even be more latency due to increased server strain and calls. This means even more weasels, bears, yetis or whatever animal error code has been shooting you to the title screen. Bungie servers would now have to keep track of all of your RNG rolled weapons, along with an exactly identical version for the other environment contributing to possibilities and introductions of weapon glitches caused from PvP/PvE environment change like going from Control to Strikes. It's just what would happen with separate environments being alternated so freely.
(I know this isn't necessarily ideal and has flaws, but it's just a thought to get the ball rolling in the right direction)
Now, if you've made it this far by hearing me out and not instantly downvoting me into oblivion here's the section where I say what I think should actually happen, and what would positively affect the community. It's pretty simple in that what Bungie should be doing is just opening testing up to the top level players and let them try to break the game as much as possible. This means giving the players who know the game inside and out early access to updates to mess around with in their free time. Maybe even let them broadcast it and get feedback from their twitch channels. Whatever playtesters they have currently are so tunnelvisioned by what they've implemented that they don't actually know how to play the game. I know this because when you're testing something and you know how it's supposed to work, then you're gonna do it how it's supposed to be done.
But that's not how the Destiny community rolls.
We do dumb stuff all the time. We break stuff, find glitches, exploits, etc within a few hours of a new patch dropping. Obviously we're doing something the testers are not. I've seen posts for public test servers before, and this is absolutely the balancing Destiny needs. Not separate PvP/PvE balancing.
Thanks for reading, I look forward to hearing any thoughts/comments you guys have.
TLDR: Destiny is a complicated game and D2 will inevitably be more complicated so they don't need to make it any more complicated than it has to be. Just balance the damn game the right way.
Edit: this may be the most controversial post I've made in my reddit history lol