It's an unrealistic test as pages aren't really made up of tiles of images
Generally images are the lowest priority download, so ensuring higher priority items get downloaded first is important and not all H2 implementations do it well
Its only unrealistic because so much tooling was built to avoid sending multiple files. JS tools for bundling every js file in to one, sprite sheets, using multiple domain names to get more concurrent connections. With HTTP2 we could dump so much of this.
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.
Similar arguments apply to the use of ipv6 over v4, to Linux over windows, to RISC over X86, to anything over javascript and to countless other “better” solution to problems that don’t get fully adopted because the old stuff continues to work decently enough.
Generally images are the lowest priority download, so ensuring higher priority items get downloaded first is important and not all H2 implementations do it well
https://ishttp2fastyet.com