You misunderstand. In both situations, you're making a new protocol. The only difference is you'd be making your own thing instead of adding new packet types to Wayland. And why add new packet types to Wayland if the thing you're trying to do can be done outside the Wayland socket? Best example is Pipewire and screensharing. People ask for screensharing in Wayland but it makes a lot more sense to have it in Pipewire because it can handle all the other tasks related to video streaming like format negotiation and compression. It works headless and independent of any compositor, the fact that it can also be used to do screensharing is a benefit of its design.