Leverage is a TV show; their leads don't ever KILL people, so of course death to a PC main character or primary supporting character isn't a real risk. And the people and corporations they go after, compared to those in SR, are frickin' tree-hugging total pacifists. Compared to your average Shadowrun, once they were made - and here's the thing, in Leverage they always get made - they would not have two or three guys going after Eliot with brass knuckles, they'd have a squad of 12 or 16 with suppressed SMGs and only if he's lucky and they want to question him would Eliot survive. Leverage has the presumption that even the worst bullshitter on the team (Hardison - yes, Parker is better) is more believable than common frickin' sense.
'Superhuman' here is essentially defined as being 'more than human' - and if you have eyes that can see in the dark, or cyber that lets you hit right where you want with almost any normal shot, or magic that enables you to whistle up spirits and read a person's mind, you are superhuman. Starting runners are more competent (R5-6 skills in their key abilities) than ordinary humans who do that thing for a living (3-4); they may not be superspies or military special operations, but after only a few months more of hard work (call it 10-12 runs), they may be. After that, it's a question of 'among the best in the world'.
Does this mean that every character should be ultra-focused? I don't think so; overlapping skill-sets is only to the good, and every PC should be able to do a few things relatively competently at a 3 or 4 - use a medkit (Biotech/First Aid), make a sale (Negotiation), show bloody proper courtesy (Etiquette), shoot a gun (some version of firearms), drive a getaway car (Car / Pilot Ground), use a computer (I ... don't even know what that is any more, but Data Search sort of stuff, not hacking). Every character, however, has his area to shine - face, mage, rigger, decker, street sam - and in that area he should beat the others like a kid with a bunch of pots and pans. That character should have gear (and implants) that helps the character do that thing incredibly well.
The problem - the 'power gaming' portion - comes in when your characters focus on 'their area' at the expense of the baselines. When your rigger winds up going through all 1500 rounds in his drones' weapon mounts because he can't negotiate a simple gangland territory crossing, your street sam ignores his friends' bullet holes because he can't even use a medkit, or your mage has to surrender the entire team because he was so incompetent behind the wheel that he crashed into the gatepost on the way out of the compound. Not everyone has to be instantly competent at all of those crossover skills mentioned above, but when your PCs are putting every last bit of karma and nuyen into 'their area' to the detriment of having any useful secondary/backup skill, then you have a problem.
And that's when you hit them with the 'the Vory guy will only negotiate with the Russian rigger' problem. Make the difficulty their difficulty, and maybe they'll decide 'hey, spreading a few karma around to my other skills might be a good thing ...'