I'm pretty sure hidden MMR affects your weighted RNG in TFT
If you haven't noticed by now the RNG isn't exactly random. If you're building towards something it's less likely that you'll see it. I can go a whole game seeing two garens while trying to build nobles.
I'm consistently in top 4 fighting people with way more 2 and 3 stars than me and I'm still doing fine.
I've asked other people and they said their RNG was completely different on side accounts so it begs the question if your hidden MMR slows you down.
Edit: Wanting to see if this is plaguing other people too for reassurance. I'm having less fun now that my RNG weight seems to be in the absolute toilet. It's like if the game throws Yordle Elementalist Dragons at me then I have to build it because I'm not going to see anything that I'm building that game.