i may be wrong here, but if i remember correctly, in ech, essentially our first communication is done with some central server (which as of now is mostly cloudflare) and then they make some connection with target server, and then a channel is established between us and target. my google-fu brought me this , which is basically this only
https://cf-assets.www.cloudflare.com/zkvhlag99gkb/3C9ceBTx5AQXu8tS0lgzdF/55ea89f5a56843db15296b2b47f7b1c2/image3-17.png (https://blog.cloudflare.com/encrypted-client-hello/)
I am unfamiliar with QUIC, and quick search basically tells it is kinda like multilane highway for udp.
If I have to compare, (not a network engineer or a person who has studied networking, to me anything beyond the simple protocols seems magic), QUIC seems like a techt which is only used after you have made connection with target, so its implementation is google independent (they seem to be lead developers for this). Whereas in ECH, cloudflare are the primary devs, but also the holder for the public keys (someone else can also be the holder, but i dont know of any other provider currently, maybe my lack of knowledge here)
Essentially just an extension of your point that implementation is lacking
i dont really have anything to add or ask, but appreciate what seems like unicode character in your username.