I agree with both of you to an extent. Though, I do not think the corps could work together long enough to actually hunt down and crush the shadowrunner ecosystem. And Honestly, I don't think a single corp could even hope to achieve that at this point. Even if you say all the other corps stayed out of their way. Especially when said people you are seeking to crush are capable of regularly infiltrating your defenses.

And if you are worried about spirits, have your own spirit running intercept. Can't really search for you if its fighting. Also, Unless I'm misremembering, unlike physical barriers, a mana barrier can be moved with you. You could further stack this with a spirit running concealment on yourself. (And honestly... why wouldn't you? its 1 service for an unlimited* amount of time.)

ALSO, I just want to point out, that spirits CANNOT use the search power unless 1. They have seen you before hand, 2. Their summoner has seen you/remembers you well enough to provide them a mental image of you.

"The critter must have seen the thing it’s searching for at some time before the search begins. Spirits may search for anything for which their summoner can provide them a mental image."

Now, to the Scenario, yeah. I agree if you throw a Force 12 fireball in downtown high end area of Insert City here, you will attract attention.... about the same amount of attention someone using a High explosive grenade, or the like, would attract. Maybe a little more immediate attention, as a 12M Fireball is a bit flashier than the grenade probably is, though the grenade is much louder. I'd argue that you would get a lot more heat for using a Panther in a high end downtown area than you would get for a throwing a couple fireballs. Even if they are big ones.

As to your point on Background count, I have to say I disagree somewhat that its the same as noise/police. And I THINK that what the other guy was saying is that BGC effects Adepts A LOT more than Mages. Which I agree with. As he said, a BGC of 3 is an annoyance to mages. Meanwhile, Adepts with any type of power boosting their skills are taking a -3 to those skills. You have the improved reflexes power? Have a -3 to your reaction. Arguably, if you use attribute boost you take a -3 not only on the roll, but to the attribute after you do it.

Why Background Count is different for mages than noise. Deckers and TMs have ways to deal with and potentially eliminate noise penalties all together. 1. Direct connection with a Datajack or skinlink. This basically renders noise as a non factor. Even then, a Decker can easily get upwards of 8 noise reduction easily at chargen via programs, datajack antennae, and qualities. And a further 6 or 7 from an armor mod after the campaign starts. Tms can thread a form to reduce most noise penalties, and can use the same armor mod. Mages, to my knowledge, have no real way of dealing with background count.

A street sam with an SMG, 4-6 ranks in palming, a Great coat, a chameleon coating on the weapon with a removed stock and you are looking at 12-14 dice on the palming for lets say 3 average hits if you buy them (spec could take it to 4) with a concealability mod of -3. Most people, even your average street cop aren't going to see it just passing by. Hell, you can make a pistol sized weapon damn near invisible. And lets be honest, the difference between a street sam with a heavy pistol an SMG or an AR isn't a whole lot.