Without meaning to sound dismissive, because I'm really not intending to, there's also the possibility that you've gotten worse after enough time using them. You're treating yourself as a constant in this, but man cannot walk in the same river twice.

This is such a silly response when "You've gotten better at using them and know how to work around their flaws now." is right there and seems a lot more plausible.

That's a possibility, but I doubt it. I've been programming for 35 years and know what I like in code. I've also previously maintained a long review prompt in which I tell the models all the ways in which they get things wrong and to go look for/fix those problems. But those review passes now don't take as long because there are fewer such problems to begin with.

In particular GPT 5.4 is much better at not duplicating code unnecessarily. It'll take the time to refactor, to search for pre-existing utility functions, etc.