Mercury is an interesting case. While there are some moons that are larger than it, they aren’t nearly as dense. Its surface gravity is only a little less than Mars, even though its smaller in size, so it has potential for orbital domination. The Sun certainly helps in keeping other objects clear, but that shouldn’t be part of the equation, if Mercury qualifies as a planet it should be able to do it in any orbit. I wonder if you put Mercury where Ceres is and ran for a few millennia what would happen?