What you wrote aligns with my experience so far.
It's fast and easy to get something working, but in a number of cases it (Opus) just gets stuck 'spinning' and no number of prompts is going to fix that.
Moreover - when creating things from scratch it tends to use average/insecure/ inefficient approaches that later take a lot of time to fix.
The whole thing reminds me a bit of the many RAD tools that were supposed to 'solve' programming. While it was easy to start and produce something with those tools, at some point you started spending way too much time working around the limitations and wished you started from scratch without it.
Would running an application with chosen GC, subtracting GC time reported by methods You introduced, and then comparing with Epsilong-based run be a good estimate of barrier overhead ?
The whole thing reminds me a bit of the many RAD tools that were supposed to 'solve' programming. While it was easy to start and produce something with those tools, at some point you started spending way too much time working around the limitations and wished you started from scratch without it.