Luck is obviously a component, but style of run matters too. You could have done well over 15m by now if you did a daily 50k run without Aminon.
I don't know that anyone has a high-quality dataset to say exactly the rate of cases+1 from various sources, but my impression was that they were well under 10% from downstairs bosses and even lower everywhere else. A group doing 9/9 runs probably gets 3x as many old cases +1 per gallimaufry earned as a group doing 8 boss and never touching Aminon.
If you're specifically comparing to a soloer or small group getting coffers, they also might get 3-4x more earring probability per gallimaufry earned than an 8 boss group[but it will take them MANY more runs to get that amount of galli].
This isn't to negate the fact that there is statistically going to be an extreme level of variance in a system like this (chance of old case +1, chance of ear box +2, chance of perfect augment). Multiple very low rate steps means there will absolutely be people getting far more or fewer rewards than the average.
The only real takeaway is that Aminon is far and away the best way to get earring chances. If you're a group doing 8 boss every day and you are absolutely not able to manage 9/9, you should really look into doing a more rotation-style run like:
Aminon + 4-6 boss -> 8boss -> Aminon + 4-6 boss -> 8boss -> etc.
This would still be more galli than what you're doing now, and it'd give a huge increase to your earring chances.
Or, if you're good with flexibility you could do:
Aminon + 4boss -> 4boss + aminon -> 8boss -> Aminon + 4boss -> etc.
This would be even better because you'd get Aminon 2/3 or 3/4 runs or whatever depending how many bosses you can fit in with him.