I spent about 15 minutes trying to create a custom Distance function in Google Sheets:

    const DISTANCE = function(a, b) {
      [latA, lonA] = a.split(",");
      [latB, lonB] = b.split(",");
      latA=parseFloat(latA);
      lonA=parseFloat(lonA);
      latB=parseFloat(latB);
      lonB=parseFloat(lonB);
  
      return 2 * 6371000 * ASIN(SQRT((SIN((latB*(3.14159/180)-latA*(3.14159/180))/2))^2+COS(latB*(3.14159/180))*COS(latA*(3.14159/180))*SIN(((lonB*(3.14159/180)-lonA*(3.14159/180))/2))^2))
    }

So that I could just paste concatenated "lat,lon" coords in place of the AWS region names and just compute e.g.

    =DISTANCE(A2,B1)

Into a second sheet, and then just divide the first sheet by the second sheet as a third sheet.

but I kept getting some "#NAME" error and I don't have time to figure it out.

Bad UX, Google. This should have been easy.

Better yet, you're freaking Google, why isn't there a DISTANCE("Hong Kong", "Singapore", "straightline") function?

I have to get back to work but if someone can figure the rest of this out please comment back.