From experience with Zena, this is not true at all. Opus, Fable, Gemini Flash and Pro all barely make any syntax mistakes after a little is in context, and those are caught extremely early.

The one thing I do see sometimes is that agents sometimes don't take advantage of added features, but that's partially because the Zena code base doesn't use them as much yet. I'm working on skills and linter-based suggestions to use better patterns.