there are 132 champins
The odds of one person getting any one of these champions is 1/132 or 0.76%
The game "randomly" chooses 10 champs but then there is also a 1 in 10 or 10% chance that any one particular player will actually get said champion and no matter who rolls there never seems to be any duplicates. This means that 30 champs would have to be on the roster so to speak to keep this from happening.
So there's a 0.76 chance that you'll get the champ and then theres the fact you got the champ without any rolls and then theres the fact you got the champ multiple times in a row.
I may be doing this wrong but I believe that means that the chance of getting a particular champ is far lower than a fraction of a percent unless the system is rigged or broken.
Now that I think about it I wonder if alternate accounts can raise your odds of getting certain champs