In update 13, all weapons have gained the "threat" stat, but I am confused as to what exactly this means. What does the "threat" stat do, exactly?
The threat stat affects how menacing you are, making it more likely for you to suppress enemies. This means that they tend to duck for cover and roll around when you shoot at them rather than return fire. This is useful for keeping them from hurting your teammates as they perform mission-critical objectives and is especially useful for crossing otherwise dangerous pathways, such as the street in front of the bank.
Since an Enforcer naturally gains more threat as part of their passive skills as well as through the Oppressor skill, generating large amounts of threat and suppressing enemies tends to be their forte . Certain mods also increase your threat, such as the Stubby muzzle mod.