I'm talking about emergency improvisation here. If you have the foresight, the inspiration and the time to do it, then you can create the NPC according to your liking. If not, taking the baseline stats and modifying them on the fly can get you out of a tight spot.
Furthermore, the assessment of threat levels is a highly subjective endeavor. Personally, I see the real danger of gangs and syndicates more in their strenght of numbers and their social clout. If someone packs Move-by-Wire and a LMG, the average gang should go down hard if caught unprepared. But the people in the area will have to suffer for it, so you can kiss your Street Cred good bye. And any survivors, affiliates and allies will be back with a vengance. Thus, they are still dangerous for the runners, but on a wholly different level.
But that's just my game, of course - and yet another reason why generic stats are a difficult thing.