Axios doesn't control what protocol is used, the browser and the server will negotitate a suitable protocol and version, which the browser will transparently use for XHR (which Axios use under the hood). Don't confuse multiplexing with pipelining which was introduced in HTTP/1.1. Multiplexing is a much better solution than pipelining to counter head-of-line blocking, since large or slow responses will delay subsequent requests while multiplexing allows parallel response/request communication.

I do agree that waterfall-style requests are more prominent with a REST structure, and that something like GraphQL could solve that - but GraphQL seems largely incompatible with how many develop web apps today; smaller components that request their own data. I'm also unsure how compatible a dynamic query language like GraphQL is with denormalized databases like Cassandra or ScyllaDB where you can't model your data before you've established what queries your site/app will perform. I've yet to see a codebase where the REST waterfall problem is a huge problem though.

Note that I too dislike how slow websites are these days, and much prefer to both build and use an entirely server-side rendered one. None of the SPAs that I know of has been a success in terms of performance; Facebook, Google Mail, Reddit's redesign, Youtube, Twitch - most of them are dreadfully slow and sluggish.