SOLUTION: Don't charge energy for the Haven-Moorcroft levels if a knight has Tier 2 clearance.
This way a knight who is happy to have finally collected 15 tokens and 2* gear won't be stopped because they ran out of Mist Energy.
The same would apply to pre-Emberlight content for Tier 3 knights.
Edit: this would be bad.
Bad solution... If that were to happen, I would only do the free levels and I would be able to play all I want, and get all the crowns I want, and become super rich... and then I would be able to buy bucket loads of energy with my crowns