Legendary Creatures - don't waste your time

Woundsealer

15 creatures, at a cost of 550 mana crystals a shot.
I only had 2 out of the 15 creatures - Odric and Sigarda.
.
So what are the chances of a duplicate?

If this is random and equally weighted for all of the cards, my chance of a repeat should be 2 out of 15.

13.333% chance of pulling a duplicate.

First pull... Sigarda.

Okay, maybe just bad luck.

Second pull... Sigarda.



1100 crystals for two duplicates in a row... 1.778% chance.

Pulling the SAME card two times in a row that I already have... 0.89%

...

Last time they "sold" mythics for crystals.

I got a duplicate of Odric for one of my 3 purchases.

These mythic sales are a complete sucker's bet in my experience.

I guess the game will now focus on seeing how many crystals I can accumulate, since the drop rates in "big box" have been equally pathetic... a single duplicate rare is my usual "loot", and we don't even need to discuss the drop rates in single 5 card packs... I'm more likely to have 2 or 3 of the same common / uncommon in a single 5 card draw than I am to get a rare or mythic in a big box.