With about five minutes of my time, I found out:
wrap_comments was introduced in 2019 [0]. There are bugs in the implementation (it breaks Markdown tables), so the option hasn't been marked as stable. Progress on the issue has been spotty.
--no-merge-sources is not trivial to re-implement [1]. The author has already explained why the flag no longer works -- Cargo integrated the command, but not all of the flags. This commit [2] explains why this functionality was removed in the first place.
Rust is open source, so the author of this blog post could improve the state of the software they care about by championing these issues. The --no-merge-sources error message even encourages you to open an issue, presumably so that the authors of Cargo can gauge the importance of certain flags/features.
You could even do something much simpler, like adding a comment to the related issues mentioning that you ran into these rough edges and that it made your life a little worse, or with a workaround that you found.
Alternatively, you can continue to write about how much free software sucks.
[0]: https://github.com/rust-lang/rustfmt/issues/3347
[1]: https://github.com/rust-lang/cargo/pull/10344
[2]: https://github.com/rust-lang/cargo/commit/3842d8e6f20067f716...