Not sure about parent, but my current bar is set by GPT-5 high in codex cli. Sonnet 4.5 doesn't quite get there in many of the use cases that are important to me. I still use sonnet for most less intelligence phases and tasks (until I get crunched by rate limits). But when it comes to writing the final coding prompt and the final verification prompt and executing a coder or a verifier that will execute and verify well it's GPT 5 high all the way. Even if sonnet is better at tool calling, GPT 5 High is just smarter and has better coding/engineering judgement and that difference is important to me. So I very much get the sentiment of not going below sonnet intelligence 4.5 for coding. It's where I draw the line too.