Shared Pool
Either the chances for a champion to be pulled within a shared pool are too high, or there are too many of them in rotation. I've honestly found so many games where nobody else is keeping or using the same champions, and it still almost never shows up. While this can be attributed to RNG, it seems to happen relatively often.
I constantly see like 4 teams using mainly assassins, or somehow 4 having hextechs at a good level, but someone else struggles to get sorcerers or shapeshifters when nobody acquires them. Making a counterplay strategy out of keeping champions away is nice in theory, but the numbers don't seem to facilitate this as a viable option, and feel more leaning towards pure RNG.
While the Tier 4 and Tier 5's feel "ok" at keeping away from people, the other tiers feel ineffective within their probability distribution to matter inside this mechanic.
tl'dr Consider buffing the ability to counterplay team comps below tier 4 by hoarding champions away from others, even if it doesn't benefit you (coin investment for counter rather than just plus), while having scaling returns on diminishing probability to the type being held.