It's "meta". But mostly because a full red build is as string as ever, doesn't have any downside, and rifles are the sweet spot between defense, distance, burst damage and so on.
I have my Ravenous build with Braced because the huge amount of handling it gives actually breaks the weapon. Short explanation: the Ravenous has two barrels and shoots two ammo per trigger press - you have to change shoulder periodically to trigger the different debuffs. Point is, the crosshair has actually 2 dots, one per barrel, and stacks go up one per actual hit.
Braced is fun: with so much handling the two dots overlap. Meaning you're shooting like a regular rifle and get double stacks EVERY SINGLE HIT. Meaning you can swap shoulder twice as fast and proc way more explosions (which i've seen to hit for like 6.5 up to 9 millions).
Best build ever lol.
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Chameleon AR. It's pretty strong, because it has an insane RoF. If you're able to juggle the body shots/headshots buffs, it's hella strong. I don't liek the playstyle though, it's more like using an SMG than an AR.
As for exotics drops: most of them have a specific drop location or they need to be crafted. Once "unlocked" (dropped for the first time or crafted), they can drop from any location that can award exotics.
EDIT: i got also the Scorpio build done, it's insanely fun. Dangerous as hell but fun.