Let's take a locksmith, a plumber, an architect, an electrician, a carpenter, a roofer, and a good old fashioned handyperson.
The locksmith won't do any house wiring.
The plumber won't be patching a leaky roof.
The architect won't be changing the cylinder in the lock.
The carpenter won't be fixing any leaky pipes.
The roofer won't be designing the house.
The good old fashioned handyperson, however, has a chance of being able to do any of those jobs. While she won't be better than any of the specialists at their given specialties, she'll certainly be more proficient than the locksmith when it comes time to wire up the circuit box, or the plumber when it's time to fix the roof. She'll also be more proficient than the architect when it comes time to put a new cylinder in the lock. Not to mention the carpenter and the roofer.
What does this have to do with Anarchy Online, you ask?
Here's a planet named Rubi-Ka. Let's populate it with a bunch of specialist classes, and one generalist class.
And there is the "overpowered" adventurer in Anarchy Online.
Can't heal better than the doctor.
Can't tank better than the enforcer or soldier.
Can't calm crowds like the bureaucrat, trader, or nanotechnician.
Can't outdamage the shade, martial artist, or soldier.
Can do a damn good job at healing, compared to a nanotechnician.
Can do a really good job at damaging things, compared to a doctor.
Can do a passably good job of tanking, compared to a bureaucrat.
Can calm crowds better than a shade, which is a hell of a lot better than nothing.
Which makes the adventurer an excellent profession to choose for soloing. While it won't surpass any of the other professions in a team at their given roles, the adventurer will be able to hold its own in a variety of situations. The adventurer isn't overpowered-- the other professions just aren't very capable when attempting to do things outside of their specialties.
The generalist will almost always hold an advantage over the specialist, unless competing in the specialist's given domain.
