Shared champion pool isn't fun
It's wildly inconsistent and it ruins the gameplay experience, for me personally at least.
I start to run Nobles, only for my Nobles to get taken away. Then I run assassins in hopes of being unique since the game has given me assassins constantly, only to find out that lil' Mr. RNGsus is also running assassins and has a level 3 Kat, Rengar, Kha'zix and Pyke (who also has 2 Spears and a Luden's), meanwhile the game has given me the middle finger and now it wants me to run Sorcerers or Demons. By the time there's a "unique" comp it's far too late into the game to switch up.
I legitimately struggle to even get level 2s as of TFT's first official patch, which makes me want to break my desk since I'm constantly matched against teams of full level 2s, with level 2s on their bench. Oh, and we haven't even talked about items yet, I just don't get them from creep camps, resulting in me losing to that one guy who has 5+ items by round 4-1, while I have a mere 1-2 (average items too).
Just because someone else is running a comp doesn't mean that I shouldn't be able to, that's lame. Make the game truly RNG, or give it some more organisation so that I can actually play the comps I want to try out.