Some things to remember is that Runners are generally 'better' then most of their foes. They have to be in order to just survive!
That said, the typical opposition a runner team faces will usually out number them by as high as 100:1!! Think about it... when the alarm goes off in that office building the team is raiding, what actually happens?
Well, the guards on site respond first.... these are usually your typical 'mall cops' there for show and not much else. The spider on site (if any) usually tries to confine the team by activating the mag-locks, sending drones, and using the static defenses of the building...
BUT, the call for help is the biggest issue. Better armed and armored security is on the way, and keeps coming until the threat is gone! Also the police may be notified as well, meaning just getting off the property isn't an end to the team's troubles...
In short:
First responders (light threat, 8 to 20 in total)
2 to 5 minutes later:
SWAT style opposition (moderate threat, 10 to 30 in total)
5 to 10 minutes later:
HTR style opposition (high threat, 15 to 30 in total)
Outside of building:
Police (SWAT to HTR, 20 to 60 in total)
Of course, the fire power used by the runners will also play a part... security is not going to throw shotgun armed agents against a team using magic and mini-guns :p
Also keep in mind, the runners have a limited supply of both ammo and health... stun damage (even just a box or two per encounter) add up! And ammo gets depleted quickly in a sustained gun fight... so that Gun-ho runner team could find themselves with improvised clubs by the time they get to their escape route.
Also remember that security isn't stupid, they are not going to line up and stay static targets to be shot in the head one at a time. The are going to be using cover, suppressive fire to cover themselves, moving to outflank the team and catch them in overlapping fields of fire, using magic, spirits and drones to keep the runners bottled up, and anything else they can do to stay alive (cause hey, they don't wanna die either!).
Played smart, even a street gang can pose a moderate risk to a runner team in a stand up fight... professional security are well better trained (and have more back up!) Then a street gang!