With yesterday's Git update, Wine now has the ability to use a shared install of Wine Mono. This greatly reduces the disk space needed by each prefix, and it probably speeds up prefix creation as well. Those changes will be in Wine 4.6.
The .msi package will continue to work as before. We recently added /opt/wine/mono and /opt/wine/gecko to the search paths for the Mono and Gecko msi's, mainly so that third-party distro packages (such as winehq's) can install them without interfering with future official distribution packages that may be named differently. I think the commit adding this, 2f6896b14d2b1905a25b1ef55bcdc792f9fa02ac, is safe to apply to older versions.
The "shared" version of Wine Mono can be found at https://dl.winehq.org/wine/wine-mono/4.8.1/wine-mono-bin-4.8.1.tar.gz. It should be extracted to /usr/share/wine/mono or /opt/wine/mono. This will create a directory that includes the version number, so multiple versions can be installed independently. This file can also be built using the source tarball, of course.
For more details, see the release notes I put on Github: https://github.com/madewokherd/wine-mono/releases/tag/wine-mono-4.8.1