I think you're forgetting a key aspect of tiering: Tiers are decided based on
How much a pokemon is used, not how good a pokemon is or isn't. We can ban Mawilite and Pinsirite from UU, but it won't change anything because the two of them are still very popular pokemon. If you look at
this thread right here, you'll notice anything BELOW 3.4% usage is what fell to the UU tier. Pinsir and Mawile have MORE usage than this, so even if we ban their items,
they will still be in OU because enough people use them. I'm sure Mawile without Mawilite would fit just fine in UU without being overpowered, but because tiers are decided based on
how much a pokemon is used, it won't drop to UU. It's just like Last generation where people really wanted Donphan and Metagross to drop to UU because they would have fit perfectly in the tier, but they were popular enough to stay in OU.