Firstly, I think 5 dice to shoot is really low, even for regular rent-a-cops. I asume anyone paying for their lifestyle with a gun in hand (even if they don't usually use it) will have a competent agility of 3, a skill value of about 2 (possibly even 3 in better trained facilities), a skill specialisation for the gun they use on duty (which is usually the only one they wield, why
wouldn't they specialise?) and a smartlink, as those are dirt cheap and greatly amplify their combat ability.
That comes out at about 9 dice, which is the mid-level mook standard in our groups.
Secondly, a corpsec squad doesn't have to actively call for backup. as soon as they're under fire, about a bazillion sensors will detect the gunfire, the guys in their field of vision (they're wearing cheap vision enhancements slaved to a security node, don't they? Noticing stuff is part of their job. The more important part, even) and their rapidly dropping lifesign (curtesy of a biomonitor embedded in their uniform). Add the fact that a mental cry for help via wireless is a free action and it doesn't matter if none of them are conscious at the start of the second round; the corp is alerted.
Now, in "our" corporate world, the regular corpsec patrols don't have mages in them at all. The mages patrol on the astral and on their own. That way they are much more mobile and less easy to disable.
Those grunt patrols are usually almost uncybered, if at all. Most of the useful stuff they carry around, as it's easier to keep SOTA and transfer to the next guy doing the same job that way. A smartlink, perception enhancements, access to the security system (usually via trodes embedded into the helmet) is all they really need. The corps know that those squad can't stop a professional runner team anyway, their job is merely to spot them. No need to waste too much money on them.
The guys getting called if an intrusion is detected are usually trained for firefights with professional criminals. They usually have an agility of 4, a skill of 3 or 4, a specialisation on their regular duty gun and a smartlink, adding up to 11-12 dice.
They almost always have a mage with them, as counterspelling is vital against criminal spellcasters.
They have backup from at least one spyder, controlling half a dozen drones or more. Drones are a lot cheaper than human security personell, so they're a good way to boost numbers and impervious to small arms fire to boot.
Most of the guys in the squad have some way to boost their reflexes, as fighting a cybersamurai otherwise is really difficult. At the low end, it's a drug enhaler, usually (second hand) wired reflexes. Having a boost of more than a single IP is really rare.
They may have ware to help them resist damage, but a heavy armor is a lot cheaper and usually sufficent.
They may have ware to raise their shooting dice pool, but usually not more than 1 or 2 dice at most. Training up another member for each squad is usually more cost efficient.
All in all, they aren't all that cybered up, either. I figure anything above 25k

is bad business sense, as it's cheaper to just hire another guy.
Now, those guys send out to geek runner that became to much of a PITA or are suspected to own any valuable paydata still, they get all the cool bling. The corps produce that stuff, they pay a fraction of the market value. AND they're rich. Don't mess with those guys.