Hi all, I discovered this problem back in June with the help of the guys on IRC. The guy who helped me discover the root of the problem went on to discuss with one of the TUs about this problem and the solution for it. IIRC, Lukas was on holiday at the time, so he wasn't pestered with it at the time :)
Three to four months later and nothing seems to have changed, so I thought I'd start a paper trail and bring this to the attention of a few more people.
I committed changes to an already-established AUR package, and attempted to push these commits. Running `git push` on my slow connection just hangs. 'Impatient me' killed it after 5 minutes of hanging. Trying to push from a faster connection, I found it uploaded almost instantly. Setting GIT_TRACE_PACKET=1 when running `git push` showed up a (warning: large) log  showing that git is being sent a bunch of refs (?), presumably for packages which aren't even mine.
On a slow connection, this makes updating AUR packages to impossible. It takes a solid 20 minutes for the push to complete for me. I won't maintain AUR packages if this is the way it's going to be. Even though faster connections solve the time problem, it then becomes an issue of the amount of data transferred needlessly.
Why is this happening? IIRC, the IRC folk mentioned something about the underlying structure of the git repository at the AUR end, but I don't know enough about this stuff to say either way.
Log, xzipped for size reasons. Unpacks to ~82 000 lines.  https://ptpb.pw/XmET