Handguns need a lot of feats to work, and those feats have quite high perception requirements, like 10 Per for Sharpshooter or 11 Per for Scrutinous. With perception stat that high, Versatility is not needed at all, perception already provides a big bonus to Guns skill.
SMGs are quite perfect for Versatility, because max. 6 Per is required for the Suppressive Fire feat. The Suppressive Fire feat is usually comboed with the Opportunist feat for a free 15% damage bonus against organic targets for burst builds. Other than that, the only core feats that are required for SMGs is Spec Ops, which require 6 Agi, and Commando, which requires 80 Guns skill. In fact, in my own theorycrafting I would ditch Suppressive Fire as 15% damage is not really game changing (while Spec Ops is), and dump Per all the way to 3, thus saving valuable attribute points for other stats.
Reply to Dismas in the Shotgun + Claymore thread:
Versatility is good for weapons that do not have many feat requirements. For example, I've played sledgehammers too much to know that sledgehammers do not need any supporting feats at all. So a LMG/Miniguns build, which already has the strength required for sledgehammers, can use Versatility to be able to use sledgehammers. (But if your strength is already that high why not just invest skill points into melee and skip the feat point and specialization points) So, SMGs is another candidate, as it only requires 2 core feats, Spec Ops and Commando, of which Commando does not even have attribute requirements. The Stunner is another good candidate for Versatility, foregoing feats like Point Shot, and relying on extreme Dex investment to minimize its ap cost.