You do not close off character types by choosing to only play hypercompetent or competent characters.
That bolded part is to me the big key. The assertion that limiting yourself to merely hypercompetent concepts limits a lot of perfectly viable concepts is one I fully agree with, but most of the concepts one would actually consider using as a PC become perfectly acceptable when one adds that bolded part of your statement. A character doesn't have to be the absolute best in their chosen field, which a great many people on the boards tend to argue for, and that argument does have a lot of problems. Still, I also don't see many players making characters that completely suck in their primary focus either. Even in the old days when stats and abilities were a lot more restricted, most people still generally tried to play characters that had a reasonable chance of success in most typical scenarios. So it's a case of finding that sweet spot where the mechanics are balanced with and support the non-mechanics aspects of the character. Too much of either, and the character usually doesn't work too well for more than an adventure or two.