Is it necessary to download the native inputs while installing packages?

[Fis Trivial <ybbs.daans@hotmail.com>]

The network connections to hydra is bad at day time from where I am, the
download speed is about 10kB/s, I can only work with guix at night.
And sometimes I use guix --fallback option(like texlive), guix will redirect to
the upstream download link. Chances are the upstream has even worse network
bandwidth, then I have to manually find a mirror of that particular upstream
and use `guix download`.

In the case of *texlive-texmf*, it serves mostly as a build dependence. To make
things even less convenient, most of the mirror site only store its ISO
package, not the tar ball used in guix package.

So, I gotta wonder, can we just download the normal inputs and propagated
inputs from hydra while installing packages? Would that break something like
the functional property of guix?