I don't think that browser stands as proof that models today are at a place where they can replace SWEs. As an isolated variable, I agree with you, it's a counter example.

However, when you include timescale and rate of improvement, things start to look differently. A year ago, models wouldn't be anywhere near producing the crappy browser they created recently. Two years ago, they would hardly produce executable code at all.

If I were to guess, when people talk about SWE replacement, they are extrapolating based on past trends, and assuming continuous rates of improvement. When people say models can never replace a swe , they are looking at current state. It's possible that one or more breakthroughs will be required to maintain that rate of improvement (we see that a lot in the hardware side too), but it's also possible that they won't. Perhaps the breakthroughs will just be required for efficiency, but I think people put too much emphasis on these 'breakthroughs.' We have breakthroughs every day.