Why does Ne have a lower boiling point than CH4? Since they both only have dispersion forces, ...
Not all dispersion forces are created equal. Mass is often used as a surrogate for size, which is the more important consideration. Neon may weigh more, but methane is bigger. It's electrons are more diffuse, it is more polarizeable, and hence the magnitude of its dispersion forces are larger. It is more sticky as a result, and thus takes more energy to boil.
That's my hand-waving argument, anyway.