This is beyond bananas to me given that I regularly see codex high and Gpt-5-high both fail to create basic react code slightly off the normal distribution.
Quality varies a lot based on what you're doing, how you prompt it, how you orchestrate it, and how you babysit and correct it. I haven't seen anything I'd call senior, but I have seen it, for some classes of tasks, turn this particular engineer into many seniors. I still have to supply all the heavy lifting (here's the concurrency model, how you'll ensure exactly-once-delivery, particular functions and classes you definitely want, a few common pitfalls to avoid, etc), but then it can flesh out the details extremely well.
Today I was trying to get it to temporarily shim in for development and consume the value of a redux store via merely putting a default in the reducer. Depending on that value, the application would present different state.
It failed to accomplish this and added a disgusting amount of defensive nonsense code in my saga, reducer and component to ensure the value was there. It took me a very short time to correct it but just watching it completely fail at this task was borderline absurd.