ARAM Biased Toward Free Week Champions

I almost only play ARAM and I'm starting to notice it seems biased toward the free week champions, to the point of getting them multiple times in a row instead of a champion that I actually own. This doesn't always take place because people dodge or I will dodge as well if I get the same champion 2 or 3 times in a row.

I own 40 champions, and there are 10 free week champions. This means ignoring the other players' owned champions, on average I should only get a free week champion about 20% of the time. Considering everyone else can also get the free week champions, it should actually be a lot lower than 20%. It seems WAY higher than this, as most of the time I get a free week champion instead of the ones I own. It gets so bad at certain times that I've had to dodge because I refuse to play Kayle 3 times in a row, even if she is good in ARAM, I just find her incredibly boring aside from her ult.

I'd be fine with them favoring free week champions if they would put some kind of prevention so you don't get a champion multiple times in a row. I enjoy getting a random champion and getting the same one 2 or 3 times in a row is just not fun.

It seems they either have a bad random generation seed or the free week champions are favored. Getting the same result from a random number multiple times in a row is usually indicative of a bad random seed being used.