Are you unsure what "agentic" means? Generically, agency means, more or less, being able to do things. An agentic AI program (ChatGPT in agentic mode, OpenClaw, Claude code) can take actions without being controlled by humans. This is also sometimes called an autonomous agent, but "agentic" has become the dominant term over last year or two.
If you were to try something like Claude code, for example, you would see that it can run shell commands, grep through a source tree, edit files, run git commands, compile, execute, review output, edit code, compile again, etc.
Your post is confused as it assumes that LLMs looking for security vulnerabilities are -- in your words -- "LLMs can unreliably find some defective code patterns if they are obvious enough. (Remember, they cannot do deduction, just statistical pattern recognition. Too much noise or too far from the template and they fail."
That is false. The LLM models in an agentic system are doing more than just looking for "defective code patterns."
LLMs can perform source code level analysis, but they can also, in agentic mode, run fuzzing tools, scan for open ports, write a custom program to attempt to fuzz or exploit an open port, review the output, modify the code to try again, compile, repeat, and so forth. Multiple instances of agentic AIs can do this for many hours and more.
As I've said multiple times before Gweihir, I really don't know if you're trolling or not. You've seemed at least somewhat informed before, so I'm really surprised you didn't know what agentic means, or what has been possible with these tools. ChatGPT agent mode has been out for about a year, and Claude code for a bit longer.