[thaumasiotes]

> The better argument for Amazon is that "Everyday Sling" is too generic of language similar to "Daypacks,"

I don't really agree with that, because the "everyday sling" is not a sling, it's a container. It would appear to be a fanny pack supported by your shoulder instead of your waist.

A sling is a piece of cloth which supports something against gravity; the major applications are holding an injured arm and holding a baby. See https://www.merriam-webster.com/dictionary/sling ; the ordinary sense is noun 2(a), and there is no sense that includes a container.