IMHO, yes, because D&D is a roleplaying game, not a wargame. The ability to play a PC who is not a genius but who is still a Wizard is a fascinating role to play. Not everyone thinks so, clearly, but I also know from seeing the PCs of other players that I'm not alone in this.
Like I said upthread, I found those PCs to be very interesting. And they contributed to the party as much as anyone else, just not in expected ways.
One could make an Illusionist with 15 Int and 18CHA. Maybe he wasn't smart enough to go to MIT (Magical Insitute of Technology), but his way with people (CHA) seriously amps up his illusions to decieve people and get his way.