Python cryptography, Rust, and Gentoo

Many of these problems already have solutions and haven't really been that big of a deal in the past. autoconf and Cmake have existed for a long time.

It's hard to avoid the issues with Windows/iOS/Android but if you're developing such an application you are probably not using C. Windows has always had a hellish story for libraries.

Firefox, for one, is distributed by many in an unvendored form.

But the overall theme is that the libraries you are using (or not) need help. If a library you want to use is good, and well maintained but not packaged, help them package it. If an algorithm isn't in a library, find an existing library that is a good fit and add to it (or, in the worst case start a new library, preferably that contains a lot more than just one algorithm). Or maybe the benefits of the latest and greatest compression algorithm are outweighed by older ones due to their accessibility. Develop with library versions that are commonly available, not the latest and greatest. Wait for features to mature (and possibly help them mature) before depending on them. If distros don't package a static library of something, send a patch so they can. Ultimately doing all this work allows you to write software that can be included in a distro and that should be the long term goal that is by far the easiest for all your users and easiest for the people that end up maintaining your software.

There is an awfully large amount of well written C software that has been written this way, has stood the test of time and will likely be around for a long time to come.

Yes, this can take more time and may mean you have to do more work in the short term, or wait for new features to percolate through the process. But the long term end result is a more sustainable ecosystem with a lot less work over the entire community. Vendoring something might make less work for you in the moment, but is more work for other people (or even your future self) down the line and doesn't solve anything for other people with the same problems as you.

If you want to write brittle broken software that needs constant attention and maybe doesn't even work at all in a few years, then yes, go ahead and keep doing things this way. Those that engineer things properly will still be around, still making constant progress.