Mythology Cap Is Unnecessary
Let's say the average good time it takes to run an AK is like 40 minutes. At 40 myths per AK for that. And these values:
head - 495
body - 825
hands - 495
legs - 825
feet - 495
Relic - 900
Total for one class: 4035
Total for all classes: 36315
so 36315 total Mythology for just the AF2 and Relic+1 for each class. That's ignoring rings, neck, wrist, and belt.
At about 40 myths per AK that means it takes a total of 907.875 (rounding up to 908 cause you can't do only part of a run and get myths) AK runs. Since I said roughly 40 minutes per run it would be back up to the number 36320 minutes, which is roughly 605.33333 (repeating) hours to do it all. That's about 25 days STRAIGHT of playing to get full AF2 and Relic+1 for every class. That isn't including clearing coils. That isn't including doing farming/grinding/whatnot for crafting classes. Ya, I'm pretty sure there's enough content for people to keep playing before their next patch that they don't need to put a weekly cap.