You seem to have pulled this number out of thin air, and I cannot see a scenario where this is true.
Let's pretend you sell 300,000 units at $0.99 with the Unity Personal Plan.
Units: 300,000
Gross: $297,000
Unity Fee: $20,000
That puts unity at 6.7%. The issue isn't Unity, it's the developers bad business model for charging $0.99 while opting to use Unity.