I think the junior thing started ~24, early ~25. Because back then the level of the current models was at or above that level, with somewhat flaky reliability. In the past year that's changed. We are now at "mostly reliable" in any junior-level stuff, and "surprisingly capable, maybe still needs some hand-holding" at advanced / senior-level stuff. And somewhat super-human if the problem is easily verifiable in a feedback loop (see the atcoder stuff).

Not my experience.

It's junior level coding and maybe senior level advising, but even then only when clearly directed with the right questions and guardrails.

As an autonomous thing? Junior at best.

That's why I think it's extremely helpful for seniors: with proper guidance, it really boosts your productivity, writing notable parts of the code.