I mean, it is possible for randomized selection to produce a lot of repeats.
I do, however, believe there is more to the algorithm than they let on. I not only get tons of repeats, but I always get at least 4 of the 'Free for the week' champions in the lobby. It is like clockwork and they 'magically' never return the following week.
I 'get' that they need to sell champs/skins to keep the game going, but don't say it is 100% random when it would seem there is at least a LITTLE something more going on under the hood.
I wish they did something with re-rolls as well that wouldn't let you re-roll the original champ you rolled on. I've RR'd then RR'd again and gotten the original champ I RR'd on.
I would also like it to not allow a champ you have played in the last 5 games or 7 days (in the event you haven't played 5 games in the last week). I can't tell you how many times I've RR'd and its like oh...Rengar...again....