Make an installer instead the usual zip pack?
The data into the installer can be in 7z
during the install process the data can be converted in zip.

So we can save the 'fast' time in loading data for the game
and save 150 mb to download for user with slow connection.
Sure the installation time is a bit longer but imho not a high cost to pay

We cannot make a platform independent installer, so no.

However, a pk3 transfer tool that compresses it as uncompressed data, 7zipped, over the wire could be neat. Should be accompanied with an update tool, of course.

The main reason for the zip pack is that it is one download for all supported platforms. This really should not change. Optionally offering a separate download method, that saves some bandwidth, however would be great.