I'd suggest: new accounts are read-only for at least a week. Then they can comment (rate limited at first, gradually relaxed) and vote, and then after some additional amount of time and/or karma they can submit a post. Maybe some of these mechanisms are already in place? Bots can probably game this too but drive-by bots maybe won't be patient enough.

If that were to happen, I'd also suggest that comments from fresh accounts should also have URLs deleted or disabled.

I'm surprised posts aren't restricted a bit more. Maybe that's just my old school "lurk moar" mentality, but I feel like I really need to understand the vibes of a community before I start to contribute posts to it.