That entirely depends on whether a “smart enough” model is a genius or where that cutoff is.

To your second question, a clear plateau would be a piece of software that is 100% secure, without vulnerabilities. Since that’s impossible for anything more than a trivially simple program, particularly when you consider an ecosystem, I think there won’t be a plateau. If you use model A to secure program Dog, smarter model B could find a vulnerability in Dog or just skip to attacking Dog’s OS, firmware, etc.