Earlier quoted context omitted.
No, not writing everything in assembler, this isn't about high or low level. It's about writing things yourself for what you actually need. Because most of the complexity comes from code (esp. libraries and drivers) trying to solve a larger problem than you actually have. That's the same reason why, when you follow that logic, you eventually write your own Forth. Not because it fun. Not because you want to learn abou…
at least we can get rid of the bloated web apps once everyone begins to do so...but would it be possible if libaries are written in a way that it's easy to just integrate just a portion into existing code?
The difference I'm drawing being, libraries just provide a mess of utility functions. Theoretically, even if your compiler won't strip the library stuff you don't need, you'd be able to take just the bits you need by copy/pasting a relatively small volume of code. And dropping the library would be a small change, that just requires finding replacements for the functions and classes you were using.
Frameworks tend to involve some Grand Unifying Abstraction that you need to inherit from, and that gets imposed on your own code. Things tend to be so tangled together at a conceptual level that it's not really possible to use them in an a la carte manner. Migrating off of a framework tends to require more-or-less a rewrite of all the code that interacts with it.
To take some Web examples: jQuery's more on the library side of things. D3 is more of a framework. React is very much a framework.