It's simply the easiest weapon to use is all and if you get up close and personal it's really not an issue. The damage is caused by Focus fire and the Suros Regime perk working in concert but the Suros perk was nerfed to a normal Glass half full with healing. What makes it so easy to use it the stability as well but you can easily outgun it if you have enough skill at getting headshots which the Suros excels at.
Yes I'll admit...I use the Soros in iron banner. I aim high and plug away. If i got the high ground i win 80 to 90% of the time. You know what kills me....well placed specials, grenades, shotguns, being out numbered (sometimes), heavy weapons, and the Vex myth. Take it for what you want, but lesson of the day run in packs with a shoty. That's my advice.