Crate rarity odds and what probability means

Proposed fixed percentages, in order Common / Uncommon / Rare / Epic / Legendary / Mythic:

Gold:    70 / 20 /  8 / 1.5 / 0.4 / 0.1
Emerald: 45 / 30 / 17 / 6   / 1.7 / 0.3
Diamond: 20 / 30 / 30 / 15  / 4   / 1

Each row totals 100%. No hidden pity, duplicate protection, donor advantage, wealth adjustment or prestige rarity bonus. Rolls are independent.

At Diamond's combined 5% Legendary/Mythic chance, twenty openings give 1 − 0.95^20 = 64.15% chance of at least one such collectible. There is still 35.85% chance of none. Mythic alone across twenty openings is 18.21%.

Twenty purchased keys cost 10,000 Larks, or 8h20m of benchmark work, and use twenty weekly purchase allowances. Event/achievement keys can add attempts. Every opening still supplies its building bundle.

A miss never makes the next roll more likely to succeed. Rarity labels do not guarantee trade value, and the model does not promise a collectible after any fixed number of attempts.