Your graphs roughly marry up with my anecdotal experience. After a while, when you know when and how to utilize LLMs/agents, coding does become more productive. There is a discernible improvement in productivity at the same quality level.

Also I notice it when the LLMs are offline. It feels a bit like when the internet connect fails. You remember the old days of lower productivity.

Of course, there is a lot of junk/silly ways to approach these tools but all tools are just a lever, and need judgement/skill to use them well.