Yeah, that's what bit me. Even Anthropic's own documentation seems to indicate that Fable is not all that great as your go to model for tasks. What it seems to excel at is a sort of leadership role because it proactively keeps all the subagents in check.
If you're not explicit in the prompt or haven't configured your environment then the default behavior is to use subagents that match the host.
You can write a skill (many have) to lead it in how to use different models and efforts for subtasks. For searching the code base, for example, I have it use Haiku, which is fast.
If you're not explicit in the prompt or haven't configured your environment then the default behavior is to use subagents that match the host.