To me it's unrealistic in the sense that it's an artificial test
Images are the lowest priority resource on the page and apart from the visual appearance aspects there are no dependencies on which order they're fetched in.
Most other resources on a page have greater side effects and and dependencies e.g. sync JS blocking the HTML parser, sync and deferred JS need to be executed in order etc.
You can saturate a last mile connection with image downloads in a way you man not be able to with other resources due to effect of the browser processing those resources.
Images are the lowest priority resource on the page and apart from the visual appearance aspects there are no dependencies on which order they're fetched in.
Most other resources on a page have greater side effects and and dependencies e.g. sync JS blocking the HTML parser, sync and deferred JS need to be executed in order etc.
You can saturate a last mile connection with image downloads in a way you man not be able to with other resources due to effect of the browser processing those resources.