ChristopherKhawand the issue with your suggestion is that extensions are not self-contained.
Unlike Wordpress for example, where each extension has its own directory with all its files, Flarum uses composer so extensions can require dependencies.
Finding out which dependencies are required, finding which version of these dependencies are compatible with the extension, and finding a set of dependencies that match all packages installed is a task only Composer can do.
Flagrow Bazaar is a package (around Composer) that does that without requiring SSH access.
Something that's not been done yet is a remote Composer tool that would use the
composer.json file to return a whole
vendor folder generated on another server. This would be a solution for servers with very limited memory.