Oh, small good news, I did some arithmetic and proved, at least to myself, the 500k number is probably too high. Here’s my logic,

The highest death toll ever from an earthquake was Shinsi, China, 16th C., where ~800k died. Contemporary accounts claimed about 3/10 of the population died.

The strength of the quake and building standards are likely similar to modern Haiti, according to some guesses on the internet, linked in another thread.

3/10 of the ~1.7 million pop of Port au Prince is ~500k. HOWEVER, we have modern medicine, armies of food, tents, water purification, etc. on the way. These factors will force that high estimate down.