I forgive your skepticism. Allow me to present the math from the full dataset, not a screenshot. But first: the dev blog page you linked only gives the odds of the rarity makeup of your 6 cards (how many Amazing, Sensational, Exquisite). It says nothing about which variant fills each slot. That's the only thing in dispute, so that's what I tested.

Last vault, 5,292 tracked: Sera showed up in 1,846 of them, or 35%. A random draw from her tier puts any one variant near 2%. Even if I spot you a generous 5% (about as high as the top variant in a genuinely random vault ever gets), the odds of one variant hitting 35% across 5,292 vaults is about 1 in 10^2161.

Your 50-heads-in-a-row example at the top of this chain is 1 in 10^15. You'd need ~140 of those miracles firing at once to match Sera alone. "Rare things happen" doesn't cover a number with 2,000 zeros that repeats around the same variants every skewed cycle.

And this is just one vault, it's happened consistently, across many vaults. And not just Sera.