I don't think so. This is already the situation. Maintainers already fix vulnerabilities when they know about them.
> On the other side there’s an attacker with a singular job and a strong incentive to do it well.
If the situation is that the attacker is focusing on a single project, the attacker will win, as they do already. But the attackers usually need to split their attention over lots of projects.
> The supposed logic is that an LLM multiplies your skill
I don't agree with that logic. Agents bring knowledge with them. That's not a multiplier. Compare how well a 12 year old can do compared to a Roman history professor on questions about Roman history when they both can use an LLM or when they both can't. The LLM will shrink the gap, not increase it.