Firstly, reposting from anywhere is actually absolutely no problem at all. You are doing a very valuable service, which is curation. Yeah, people could be going to reddit or wherever directly. But do you post everything from reddit/wherever? Of course not, because a bunch of it is shit. Shit no one else will have to wade through because of you.

In addition, you're essentially reducing reddits user count. The people that follow your small community here don't have to be on reddit anymore.

Secondly, not coming up with stuff yourself is completely normal. Who even does that, really? We're mostly all just rehashing things we saw somewhere else, combining them into something "new". I'm pretty bad at coming up with stuff myself. But that's just... Not important. My worth as a person isn't defined by what I create, so if I don't create anything, nothing bad happens. If I actually do create something, nice, if not, also nice.