On quora there is prolific nutjob who spreads misinformation about gravity claiming gravity as mass/distance² was never experimentally proved and instead claims

On quora there is prolific nutjob who spreads misinformation about gravity claiming gravity as mass/distance² was never experimentally proved and instead claims gravity is volume/distance², his responses are often quite highly ranked, e.g. 2nd answer here: https://www.quora.com/Why-is-a-lunar-orbit-unstable https://www.quora.com/Why-is-a-lunar-orbit-unstable Can you please disprove his nonsense.