I think we have to generally assume HTTPS is the "new Telnet" for protocol bootstrapping and may be so for some time to come. Everyone has HTTPS debugging tools of every level "already installed" (curl/httpie/web browsers/fiddler/etc) and are mostly already trained in them. Every language under the sun has strong HTTPS libraries. Meanwhile, HTTPS gives a nice baseline for things like security (TLS was designed for multiple protocols, but let's face it is best tested and deployed in HTTP and always has been), caching, compression, many quality-of-life and quality-of-service tools. It's so much easier to bootstrap protocols from HTTPS as a baseline than "from scratch like an Apple pie" just as HTTP and Email themselves bootstrapped from Telnet. In the post-TLS era, bootstrapping directly from Telnet doesn't seem like an easy bargain anymore and yeah there are definitely advantages to getting your TLS and a bunch of other useful features/services "for cheap as nearly free" all at once in something like HTTP/3 (even if that is inheriting possibly "a lot of complexity").