Here's why rerolling is an issue. Two things.
Grenades and Horseshoes
Shot Package
Here, follow me a minute. The only reason people dislike it is because it makes two supreme perks OBSCENELY accessible. These perks were just as overpowered as before rolling, but they became an apparent issue, leading to a meta where the ONLY setups you saw, other than quality snipers, was Exotic HC, Shot Package shotgun, G&H Rocket Launcher. If rerolling were to come back, we'd fall back into this same situation again, except maybe with full auto and kneepads and lack a diverse meta that breeds a great number of play styles rather than the obvious one that slides everyone into the same mold.
English
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Balancing. I think everyone agrees that not every perk will always be sought after, but some balancing, and maybe some more nice perks, and variety will be alive.
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FPS are inherently unbalanced. It's how it works. Perks can further unbalance. Like you said, it made the lack of balance glaring. That, however, is only because it gave access to the days new unbalanced perk.
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How is an imbalance inherent?
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The only way to totally eliminate imbalance is to give everyone the same thing. The art of the deal is how to dress it and spin other things to get diverse, not balanced gameplay. The balance everyone "wants" is actually a want for weapon diversity and diversity of play styles. Rerolling circumvents this.