yes, that would be something to figure out first

HTTP2 benefited from decades of HTTP use, and a virtually ossified protocol, making it possible to design a hyper-optimized protocol for specifically that use-case

just throwing something together with protobuf is not quite that, and has the risk that another binary optimized protocol will be needed later, and of course people will want support for all three... 😀 

(HTTP3 didn't change much compared to HTTP2, the main change is switching the transport to QUIC and pretty much all other changes are related to that, but still-)