@Riot, Is AR URF actually random or is it weighted?

I am curious what the algorithm for choosing champions is for URF. I am beginning to doubt that all champions have an equal % chance of being selected. My reason for this is that I have played ~55 games of AR URF in the past 2 weeks. Counting rerolls and champ select, I've had around 100 separate opportunities to roll champions. Yet I've only played 20-25 unique champions. I have a champ pool of 90 or so. This seems a little weird to me. More weird is that not only do I not see much diversity in my own pool, but the people I play against are always the same 25-30 champs. I have specifically had Jhin come up 8 times, Kayle 6, Morgana 6 as well, counting only my own rolls. Getting 3 champs for 20 / 100 potential picks is odd when I have ~90 to choose from.

This is why I'm starting to think it may not be equally random for all champs and may be weighted towards some. I do know that I may be playing with people who have aram / urf accounts and have limited champ pools, thus increasing the likelihood I see specific champs, but this doesn't explain why I'm not rolling more of my own pool.