Conversely, there is also no way to standardize which solution to use to the extent necessary that developers could actually rely on it producing a consistent experience across a large user-base.

You don't need standard behaviour, you just need _good_ behaviour. And if every browser does that differently, but it's appropriate to the network speed and processing capabilities, then as a dev the issue of "making sure images load appropriately" becomes as irrelevant as "making sure your webfont actually loads" has become in the modern browser landscape.