I would not say that habitual usage of complex language/jargod is indicative of incompetence. (Wow. Just *look* at my proof of example! =-)) It may, however, indicate a lack of confidence, which can make all the difference.
Thinking back to Cryptonomicon, when Stephenson digresses to describe Randy's hunt for an oral surgeon, Randy finally settles on a particular "brilliant" surgeon who is completely socially inept and, rather than insisting upon Randy signing a large waiver or explaining precisely why a minor mistake could remove all intellectual distrinction between Randy and a marmoset, he simply says "Okay." and walks out of the room.
I have to say, when Things Need to be Done, I've always preferred precisely this sort of person. They're usually socially inept because they're busy doing other, more interesting things (though it *could* be an indication of general ineptness) and they don't bother with excuses. They either can do it, or they can't, and they'll say so.

~Cybercosis