huge bankroll had nothing to do with the annual return. There are many several things to consider , one of the thing is that the house edge for investor , house edge for players and the wagered ammount in the site. The turnover is actually what you will gain as a investor and it had nothing to do with the bankroll
Since most sites allow investing on margin, bankroll shouldn't be used though but the "virtual bankroll" should be used. I tried to explain it before to OP but he seemed confused and I can't care too much to explain further. Without the "wagered" numbers it's unclear if the given numbers are correct but you should probably assume the "turnover / expected annual return" numbers are incorrect.
I see so bankroll is a definitive aspect for it too. Since you mentioned the wagered amount, I realized that there is none of it presented here and I do think that their is a flaw in the data since there is no formula presented here as well how do OP get the number of the annual return