I don't know the exact historical reasons, but I think you are onto the right answer with regards to paper sizes. Printing was much more important back when these were defined than today. And if you compare it to letter size, the aspect ratio matches better, and I am sure as Sue pointed out that having nice round numbers made more sense, so it does look like the numbers where picked to be a good fit for both monitor and paper as the prime concern

Of course, with the modern new map wizard, most templates allow you to pick values at any aspect ratio anyway.

Sorry about your job. Hope this situation normalizes soon so people can get back to their jobs, or at least have an easier time finding a new one when not everyone is trying to hunt in the same limited pool.

At least the time isn't wasted when you spend it mapping :)

Kind of. You could do the same with a solid color and the transparency effect.

Transparency in images is a common thing though, and is used in a lot of the CC3+ symbols. The advantage to have it baked into the image instead of using an effect is that you can control the transparency for each pixel of the image, while the transparency effect applies equal to the entire sheet.

These tools use a raster image for their fill, which is just a 1-pixel image with either a black and white pixel. This image is set up with built-in transparency. You'll find these fills in the fills list as Solid 10, Solid 20, ... Solid 90 and Solid White 10, ... Solid White 90, where the number indicates the opacity (10 is almost fully transparent, 90 is almost fully opaque).

When overlaid other elements in the map, the pixels below are mixed with that fill according to the transparency level of the fill, thereby serving to lighten or darken whatever they overlay.

Looks good. The main thing that seems to be missing are effects. Especially the piers look very flat on the water without some kind of shadows and/or glows or bevels to help elevate them a bit.