And the plot deepens as Tonks gets thrown into the mix. It would appear that the difference 'tween muggle-raised & wizard-raised is shown as a definite detriment to wizards. Tonks seems to have depended way too much on spell-casting ability - where she might have an advantage over Hermione - and not enough on thinking and/or physical ability. Then again, most wizards appear to be a lazy bunch.
Not necessarily physically, but lord, as a group, Wizards tend to be dim. When even the 'light' wizards can't pass in the general population... I mean you could take a member of a freshly discovered stone age hunter gatherer society and with a few weeks of observation alone would be capable of dressing him/herself like a member of what ever society he/she was transplanted to. Even if it was a spiffy color to go with his/her eyes he/she would know that lime green suits would have stopped being fashionable back in the '70s and weren't all that fashionable then.