As said on the other topic, average is nice but ask too much data. So yeah after some/a lot of trials (with one trial equal on succesful drop of one Mythic), you will be on the average, but it doesn’t help to know how much we need to be almost sure to obtain one Mythic.
So in resume, to have a 95% chance to drop one Mythic when he’s the only in the drop pool, it’s more or less x3 what you said: