See most of the ecosystem around React, for reference. It's idiotic that things like URL management are done in Javascript. Or form controls. I guarantee that if we stopped doing this kind of stuff, JIT wouldn't matter.
To some extent this is just saying "developers will depend upon the performance given to them", and that's true, but it's also true that as soon as things like V8 and Node appeared, JS became ubiquitous. Pandora's container, if you will.
See most of the ecosystem around modern systems software, for reference. It's idiotic that things like memory layout and bit-level hardware management are done in C abstractions. I guarantee that if we stopped doing this kind of stuff, compiler optimizations wouldn't matter.
To some extent this is just saying "developers will depend upon the performance given to them", and that's true, but it's also true that as soon as things like compilers and standard libraries appeared, C became ubiquitous. Pandora's container, if you will.
Cute, but no, not even close to a good metaphor. The C example is abstracting away complexity. The other is competely re-writing -- in duplicate -- what the platform gives you for free.
The equivalent level of idiocy in a C-related metaphor would be...I dunno...if you decided that you didn't like the way that header files worked, and decided to keep the C compiler, but build an external header-file management system in Fortran.
(It hopefully shouldn't be lost on you that this exact approach to language features has been repeatedly tried in the javascript world, including right now, with package management.)
Sites are slow because with all that excess performance they do more tracking, instead of keeping the website as-is.
Because that's the only thing business managers can come up with in that situation. It's a misaligned goal of users vs businesses.
In my opinion the "user agent" behavior of browsers is long gone, because they're not acting on behalf of their users anymore. They're acting on behalf of businesses.