How can a gun be OP when you need to think carefully about how you negotiate the map when you're using it? It dominates at one specific range and even then, if you miss the OHK then usually you're done for. By contrast, if I don't want to think, I just equip a PDW/MSMC, Dex and laser sight and it's instant easy mode.
The R870 is the gun I use on the small maps when the entire enemy team is running around with PDWs and MSMCs, laser sight, dexterity etc. Stops 'em dead and makes the game actually semi-bearable until one of the few good maps (i.e. any weapon type is equally viable) comes along.
No, it has less range and a worse spread than the Stakeout. A pump action should destroy up close imo. I'd rather see other shotties get buffed rather than have the nerf hammer take effect. Does the 870 get annoying? Yes. OP? Not even close.