I personally don't think that only commenting is a bad thing. Sure posts would be "better" content, but discussion is also a major part of what I find entertaining
I am bad at quality posts but better at comments. I'd say any way you can contribute is great. Communities require effort and reddit was as much about content from the comment section as it was the original posts.
My contributions are spamming upvotes and the occasional comment
Edit: I also occasionally indulge in downvoting posts / comments that have a lot of downvotes, even when I dont fully know what the conversation is about. Got a lot of downvotes? Have another