This argument is analogous to

[David Swan]

This argument is analogous to that been grammar descriptivists and prescriptivists. Oliver Kamm did, for some years, lay into the latter in his characteristically trenchant style in the Pedant column of The Times. IMHO, the community overwhelming thinks that 2020 is the first year of the new decade, and therefore it is the first year of the new decade. We are not talking about constants of the universe here. Nonetheless, I am willing to tolerate pedants who think otherwise. This isn’t Twitter 😉