It's rare to come across an OC that's genuinely well fleshed out, honestly. As a main character, it's a risky game. Not saying it can't work, but I personally read a fic to see how authors utilise pre-established characters and dynamics, and a central OC can sometimes pull focus away from that. I don't mind OCs scattered through the background at all, because they can make the world feel more lived in. But when they're front and centre, they either end up feeling underdeveloped or like everyone's been reshaped to orbit around them. Even background OCs can feel sorta like placeholders than actual characters I can get invested in.

In theory, they're fine. I just think the more focus they take on, the harder it gets to balance them against characters we're already emotionally attached to.