Define effective.

I doubt I'd feel good about any mage throwing less than 9 dice in drain resistance. You also want to amke sure your logic, intuition, and charisma are decent so you can roll with multiple focuses active, spot things physically ans astrally, and keep a few spirits around. With the 200 BP cap after getting your mental stats to a decent place you are frequently dumping physical stats hard. Remember 160 of your 200 BP gets you to average. Without dumping things and hard you have a whopping 40 points to make your mental stats shiny, so lets say 5,5 logic and willpower. And now oyu are just average in everything else, that sin't a tank, you aren't dodging attacks etc. Yes you can try to build the perfect character with X armor and Y spell gong all the time, but a GM can tell you no not in my game(just like he can with any other abuse) or, sure go for it and when swat teams rol out all the time against you don't blame me mr. mil spec armor.

I do think mages are too powerful, but they are damn expensive at the same time.

I do. Well that's not completely true, if a character has an appropriate contact, I multiply his Connection rating by 4 and compare that to availability to see if he even has the connects to get a piece of gear. Gina the Connect 2 gun dealer who sells small arms out the trunk of her car can score you a submachine gun, but if you want an assault cannon you'll have to deal with Uri a world class arms dealer who has contacts inside Ares and the military assuming he's even in the country. And dealing with someone like that has many strings attached.

The consequences of using that piece of gear is the character's own. However, blasting someone with a bolt in a StufferShack is about as illegal as shooting someone to death with a light pistol. Shadowrunner's actions have consequences, sure. A player of mine really wanted a Barrett; to get it he had to not just pay for it but do something during a run without the other runners knowing (long story), and they wouldn't have liked it if they found out. But in the end he got that weapon. He even used it once before he died, poor guy.

Well it only takes seconds to clean up your astral signatures, while you are doing that the Sams can be cleaning physical evidence. People can track you through a huge range of methods not just your spell signatures, and heck a lot of them don't have the duration limitation that a signature has. But yes, there should be consequences for peoples actions that are fitting for your campaign world, and they should be equally distributed along player types.

I find the concept of using the PC characters that players can make and extrapolating them as a model of the entire world's population very amusing.

The game was written to model Player Characters. Not NPCs. Any attempt to use PC mechanics to simulate the entire world is going to end in forum flame wars.

I don't care how powerful you can make any single Player Character, the moment they demonstrate their overwhelming power, the world will crush them... eventually.

How accurate is that? The mook stat blocks are laid out just like the PC stat blocks (though they use lower, or higher, BP values). I know D&D 4e specifically made NPCs and PCs work completely differently, but Shadowrun NPCs appear to be abbreviated PCs.

A result of NPC mechanics needing to interact with PC mechanics.

How do you want to measure it?

You'll have material that applies to both NPC and PC, some that applies to PC and a bit that is NPC. I'll point out that most of the material that could be considered both PC and NPC is PC focused.

NPCs don't read the rule book. Players of PCs do.