At what point is your family better off without you in it?

I'm not one of those people under the impression that the term "Family" actually means anything. Family is just a group of people that you were born into- it's not a guarantee of love or acceptance or care. All of my abusers were family, and I've long learned that the "family" people talk about doesn't really exist. Some people are just luckier than others. Thems the rules.

I've long gotten rid of the abusive family members and estranged parts of my biological family came out of the woodwork to help me recover afterwards. You could say I was surprised, and really I still don't understand it. They hardly know me. There's no reason for them to have done this, yet they have for three years.

I'm finally in the position to move out of my elder sister's house. It happens in a week and I'm stressed out of my mind, but whatever. That's life. She and I have had a tense relationship the entire time anyway thanks to my issues.

And that's kinda what this comes down to. I'm never going to be okay. I'm better than when I came to them fresh out of homelessness with a barely functional brain and afraid to even take a shower without permission, but I'm not anywhere close to okay. I'm depressed, have pretty bad anxiety and PTSD, and fail phenomenally at almost everything I do. I'm going to be playing catch up for the rest of my life and I'm incapable of being a productive member of this family. I'm not interesting, or have experiences worth sharing, or things to pass on to my nibblings, or money, or smart, or even capable of love. You could say that my humanity has -as a whole- been completely beaten out of me.

Every time I attend family events I just feel like a sideshow. Like me being there drags them all there. They're all successful, happy people and I'm over here like "Yay I made it out of bed today", and it's just...wrong. I'm not pleasant to be around, or if I am it's because I'm completely bullshitting my way through interactions and that's draining for me. I've stopped attending events after realizing that I just don't belong.

I feel like a broken wind-up toy in a room full of fancy RC cars. I can do the song and dance, but that doesn't mean it's real. They want me to participate and include me, but how do you stand next to people who are 20x better than you and always will be? I barely even feel human most days.

With me moving, I'm coming to realize that this might be it. I might not see them but once or twice a year after this, if that. If I really wanted to, I could just disappear. And I can't help but wonder if that will be best for them. I'm not really going anywhere in life, I'll never be something worth talking proudly about or become someone worth having around their kids. I'm just me, and that's not enough. Should I just let them go?

tl;dr: Family is awesome and shiny and smart and I'm a broken human being with no redeeming qualities to speak of. I'm moving out soon and wondering if it wouldn't be best for me to just remove myself from their lives and leave them to it. At what point do you just bring down people by being around them?