Why should a casual player ever finish a Mythic?
Casual players never had a shot at a relic or mythic back at 75, so why now?
I don't see anything you've said that addresses the argument I put forth. If they reduced the requirements to about 20,000 Alexandrite, the entire thing would be approximately soloable for a person with access to three acounts (minus Einherjar) in half a year. The objectives of the second quest are set up to require about half a year of effort, so asking for a disproportionate reduction in the Alexandrite requirements simply because you've already done most of the other requirements doesn't really make sense.
Also, you keep saying 6 times as expensive when you're obviously ignoring the cost of Marrows. It's more like 4 times as expensive all-told.