But this was only necessary because the binary packages for py310-cryptography did not exist on MacPorts for your platform at the time you did the upgrade. MacPorts therefore had to build from source, and that necessitates installing the compiler. Nowadays, with the appropriate binary package on macports.org, installing the Rust compiler should no longer be necessary. For example, I have successfully installed the py310-cryptography module just now off of MacPorts without rust being installed. Rust binary packages intentionally do not rely on a language runtime (only libc), whereas Rust source packages will naturally need to rely on the Rust compiler.

Building from source is always going to be more painful than installing a binary package; I have packages in MacPorts that can take hours to build from source (binaries not available, usually due to using an uncommon mix of feature flags). It's misleading to suggest, however, that the little package you installed carries 393 dependencies, when those are the dependencies of the compiler rather than the package itself.