For a junior developer, I'd say frontier models passed their standard some time ago.
No, I disagree, and now that I'm thinking about it more, quite strongly. I think frontier models passed the mediocre programmers of all seniority levels some time ago. I've worked with so many arrogant pillocks who are convinced they are the shit and will not listen to someone with domain expertise and then get pissy when they turn out to be wrong. Or worse, get political and push through an objectively broken thing.
Good juniors can drive AI really well and do good stuff. I had a summer intern the summer just gone. 2 month placement in the middle of an engineering degree. Basically gave him a problem I didn't have time to work on: you know "here's the current solution, here's what I know, this is the problem, go nuts" kind of deal. Obviously there were regular feedback sessions, but he did all the work, and used AI heavily but not religiously. And that's now part of the product. He was obviously very very junior, but I've had seniors who were less capable and flexible.
The frontier models are hit-and-miss when it comes to writing good test suites,
I've also found the mediocre are very much monkey-see-monkey do kind of programmers who write tests because those are Bet Practices and they are the Best. But they also as I say convinced they are the shit and don't appear to actually believe their code need testing really. CI is there to put the halt on all the fools they are surrounded with, not them of course, but they know they need to model Best Practices for the unwashed.
End result, a lot of programmers are shockingly bad at writing tests and basically test useless things that are easy to test and unlikely to break but don't do what's actually hard but important. This appears to be what Claude has been trained on: basically the average, on average and it tends to write long batteries of more or less meaningless tests.
Naturally good juniors aren't very good at tests initially. They're juniors, but I find it's the attitude that matter. It's not hard to convince them they might be wrong and that there's a need for testing. Or "prove to me Claude hasn't messed it up", kind of thing. I'd much rather work with an enthusiastic junior who wants to prove me, Claude or themselves wrong than a senior programmer who I have to beg to consider the notion that their code might not be perfect.
TL;DR I broadly agree, but I think Claude makes the competent/incompetent split starker, not the junior/senior split.
Currently, based on objective data comparing similar fully completed development tasks like for like, I still outperform agentic workflows using frontier models by about 25-50% on average, and I don't have to pay anyone extra fees to do that, and subjectively I also find it more engaging to work that way. So I don't really buy the hype about AIs making us all orders of magnitude more productive unless you're happy to YOLO everything forever and take the much-discussed risks that comes with.
Yes, though as you say quite a lot of stuff can be YOLO'd.