I have long suspected it, but it seems to have gotten significantly worse of late.
Every game has far too many of the same exact champions in them.
3 games in a row and only 3 champions out of the possible 15 variant are different?
That is statistically ridiculous. I wish I had access to the data to properly extrapolate how broken it is. I doubt riot will bother, since they ignore everything to do with ARAM, but a massive portion of your playerbase plays it more than SR.