Teams of specialists (at least lightly-specialised, not necessarily 2D or 1D extreme specialists) are IMO required for good RP.
And you're certainly entitled to that opinion, and I'm entitled to the opinion that "niche protected" groups lead to a lot of the group sitting around being bored while one or two people do all the cool stuff for half the session... such as our hacker spending an hour or more of real-time poking at the GM trying to get every last scrap of info out of him that can be possibly be dug up on the Matrix, to the point where I tune out and lose the plot of the job.
... ... ...
Also, what you're saying, essentially, amounts to the belief that that one single person... someone, for example, who has "earned" the title of Street Samurai... isn't supposed to be able to good at sneaking, shooting,
and hit someone with an axe, and that
no Sammie should be able to open their mouths in front of the Johnson without serious risk of embarrassing themselves.
However,
realistically, everyone that's a "serious" Shadowrunner is going to have one or two areas of focused specialization, quite a few areas of general competence, and a handful of spots where they've got no damn clue. It's not a digital CAN / CAN'T switch, but an analogue state.
Generally competent people work with other generally competent people for several reasons... 1) you generally need more than one body to get the job done, 2) having other people who can pitch in and cover the slack if Jimmy takes a stray to the head is a
good thing, 3) having more people on your side who can put bullets in the other guys is
always better, and 4) and everybody's got a slightly different "special talent"... i.e. the one skill they have at 6 and the area their Qualities are synergized to help with.
Yeah, a Street Samurai built with 1000 Karma might be able to hold their own at a meet, or act as a good wheelman in a pinch, but he's still not going to be
as good at Facing as a Face
*, or as good at Rigging as a Rigger, even if they have Influence Group 4, or a commlink and the right software. Why? Because they're not going to be "wasting" Essence on the right bits of cyberware, or Karma on Piloting beyond Pilot Ground Vehicle, or Quality points on getting the "right" qualities to max out their abilities, because that's not where they're focused.
So, yeah, if the GM is putting the GEB (Good Enough Bar) at a level where that extra 4-6 dice difference doesn't matter... yeah, it's going to mean anyone can do anything. However, that just means the GM needs to adjust their playbook.
*Of course, a dedicated "Face" should be a goddamn Pornomancer, IMO, or stick with being a Slash-Face (aka Mage/Face, TM/Face, etc). Anyone that's got a niche that narrow is just a liability unless they're good enough they can talk their way into an unscheduled meeting with Loftwyr. Getting out, of course, is another matter.