i have just been looking at the following chart. (credit to king ollie)
at this point would it not make more sense shortening the rotation by having 6 mythics in the SF each week, shortening the cycle by 50%?
Yes.
Yes, very long.
The Soulforge only allows 4 Legendaries and Four Mythics per week. Since there are so many Legendaries and Mythics, it should have its own dedicated section that allows 10 of each, especially since more of them will be added in the future.
this makes much more sense