So characters can be quirky without being flawed and vice versa. It's the quirky traits that stand out as endearing while the flaws are seen as stepping stones to maturity and awareness.
QUIRKY having or characterised by peculiar or unexpected traits /Out of the ordinary features.
e.g. Luna Lovegood
FLAWED marked, blemished or having other imperfections that createsa fault or weakness in a person's character/ personaity; mistake or shortcoming, making the characters much more real; more human.
e.g. Marvin the Paranoid Android suffers from extreme depression in The Hitchhiker's Guide to the Galaxy.
One could also argue that as an android he is also quirky.
While both types of character stimulate our imaginations, our emotions and our interest, the trick seems to be in creating characters that the reader doesn't of tire too quickly and that they can still relate to and feel some empathy for despite any apparent flaws.
It is certainly food for thought when deigning one's characters for fiction.Characters should have flaws to be well rounded and acceptably human, but how many of those characters we read are truly quirky?