In some cases I do agree to this but I create OCs (mainly in my novel series I am making) based on people that I know (friends, enemies, family, etc.)... kind of like how I see them in my own eyes... Though I can relate to this based on my main OC, Fireseeker.
I feel the same way. Each character I create either has a piece of me or an aspect I'd loved to express or at least have.
Since I really don't make OC's for fan art I create the character for stories I'd love to share with others.
Though if one of them landing in a fanfic,(which would be incredible rare since I don't really write fan fics) they'd be more of an outside observer either watching the main canon character do their thing or trying their hardest to get back to their own world; and as a side note I don't ship any of my OC's with canon characters because I don't have an interest in that, plus that fact there's a lot of potential to make an good off the wall story without some much shipping.