Gimped characters are more fun isn't a fallacy, it's an excuse.
The first reaction when directly called out on anything is a defensive excuse. I told you to do the dishes, I was busy. I told you to walk the dogs, it's my brother's turn. I thought you were going to pick up milk on the way home, the line was too long. I thought you paid for netflix, give me a break I worked overtime. Your character sucks, it's artistic. And so on.
Purposely weak characters are to cover up the humiliation of admitting to a lack of knowledge. D&D presents not only 90 some odd books to poke through and most people care to read less than one tenth of one, but it introduces a lot of paperwork and math to handle. And you need to know this stuff ASAP if you want to hang with the group right? I mean, how are you going to stand in front of a group of people you're seeking to impress so you can join them and go "I know I had all week to read it, but I didn't and I still don't know what D&D stands for. P.S. I'm an idiot can I hang out with you?"
So peer pressure to remain with the group and the defensive excuse if confronted start the problem but it doesn't end there. Now you've picked something, flaws are better for RP, and to change it is to admit you were wrong before and by extension an idiot yesterday when you offered up the excuse. You were willing to lie about it then, now you have more at stake. So now you sure the hell won't budge. Like for example take when X-Codes said Foresight was great and I said it sucked. X was locked into defending his comment or lose face by either admitting it sucks (was wrong), or didn't know of the far better things (lack of knowledge). He wasn't going to do either of those and while he came off as an argumentative idiot to some people (certainly to me till I realized what happened) but it never appeared that he didn't know what he was talking about.
"Flaws for RP" is just a big rut some person fell into rather than manning up to not knowing better. Breach the defense by not knowing them, not associating with anyone they know, and play dumb looking for them for mentor ship. Then you can steer the ship by asking focused open questions and observations which prompt them to learn the subject to maintain their superior role. Hell a play like that works will on some of those asshole bosses, and you get to high five people in the break room while talking about how your boss is a tool.