that's the point. You never know, whether you get a 100% eidolon or not. If you had the luck, which one? the most frustrating thing is that you have put everything into one element, spending tons of money for granted SSR and miracle tickets, then you never get the 100% you want. One day, you are lucky and get one, but for your crap team with only 1 SSR, even though your crap team becomes better than your ex-Main team with core SSR due to that balance-breaking Eidolon.
So for my first miracle ticket, i will choose Sol for sure, as long as I don't get her with premium ticket or jewels. I need dispel/cleanse for all my teams. The 2nd choice is cthulhu, because she is the C-frame def-reducer for any team.
Then for 2nd miracle ticket, few of the 100% eidolons should be available for a while. Maybe I would get one, so I can easily decide which core should be the choice.