Mastery/Boss Rush Concept: Like or Dislike?
Imagine a boss rush using the game’s best defenders (Kabam has the data).
Instead of giving them nodes/boost however, set them at 6* rank 3 (or higher), and give them a mastery setup. Make it itemless, but set an entry fee (units) if you must.
Then having exhausted the mastery points, give these bosses additional mastery points...even if that means full mastery of offence, defence, and proficiencies.
Show us what these bad boys/girls would look like as opponents. Maybe it will give you the data to reconsider mastery changes.