It has to clear the Kuiper belt? That's a tall order!
The reality is that the IAU definition of "planet" was a very poor decision made by people who aren't planetary scientists. The geophysical definition is much better: an object large enough to assume spherical shape from its own gravitational force acting on its constituent material, and too small to have initiated fusion and be a star.
So Pluto is a planet, as is Ceres, the Moon, and a thousand other known objects.
I understand you'd like to focus on objects in hydrostatic equilibrium. Pluto, Ceres, the Moon, and Titan are really neat, but something happens when you tell their life stories: you end up referencing one or more of the eight heavyweights. By contrast, these smaller objects just don't get referenced very much when we talk about other bodies' life stories.
The large scale structure and history of the solar system has just 8 known characters that really matter, and that's what the definition of the planet captures.