Not being a hip new language is an advantage on my books, and on many others'. PHP has been battle-tested and was once (and in a way, still is) a pillar of the internet. Stability always trumps novelty. Rust wasn't exactly created with the internet in mind, but PHP was, and it's way easier to find PHP developers than it is to find Rust developers (last time I checked).
Though the performance boost provided by Rust over PHP is not something to be ignored, though servers written in C or C++ have also been around for quite a while, and PHP still managed to trump many of them.
Without JS, you wouldn't have ad blockers and youtube could just bake their ads on the videos themselves while streaming them. Thinking about it, I don't think it's off the table for them.
I don't think the Fediverse can really provide an alternative to YouTube. The infrastructure required for the amount of data constantly being served and processed is prohibitly expensive.
I've seen a lot of native applications run way worse compared to their electron alternatives. The problem is most devs don't give a shit about code optimization.
Well, given the C projects I've worked on take hours just to compile, I think I can cut some slack for any IDE for being slow. Though I haven't used CLion a lot so I can't really speak from experience about it. Though VSCode is fast enough most of the times, and it usually only gets slower with nested macro fuckery and/or external library headers.
Playing the devil's advocate here, even IDEs like Visual Studio and IntelliJ have multiple times crashed on me or taken ages to update a single line on intellisense. C++ is simply a language where a dynamic LSP is everything but easy to make.
Someone could have hidden something malicious within your ideas, better create a whole new conceptual system.