Other diseases are worse. Measles is a lot worse, with an R0 estimated at between 12 and 18. But R0 is a measure of propagation rate in an undefended population. For most highly infectious diseases with known R0 values, we have defenses, typically vaccination which leaves the population, as a whole, a lot less vulnerable. So, in those cases, R0 is a measure of how bad things can get. Not for this new thing -- there's been no time to put defenses in place, so R0, whatever its actual value, is a measure of how bad things are.