Fable needs more... ambitious tasks than Opus to tell the difference and let me tell you the difference is there.
Simple tasks are simply saturated just like simple benchmarks. There's a level of intelligence where you simply don't need more for some things.
Yes, Fable tends to only shine when the work to be done is complex and it takes a long time. Other models wedge in different ways.
I do wish the subscription had a separate weekly allocation for rare usage.