>Is the play to plan/design/architect with a heavier model than delegate structured tasks to these smaller ones?

always has been

claude code has opusplan — uses opus while in plan mode, switches to sonnet for execution.

https://code.claude.com/docs/en/model-config#opusplan-model-...

edit: you can make it work with sonnet for planning, and haiku for execution, or any other combination you fancy to work with.

https://code.claude.com/docs/en/model-config#control-the-mod...