Having checked with a friend who was at the same time sitting in a 7K queue on the server, I decided to ask others on the Lost Ark reddit about their experiences, and received some great information from ekdud, who was familiar with the system from the other game versions: Apparently ...
This is probably the best course of action. Use either of the two official mirrors that have not yet been upgraded from HTTP to HTTPS: linuxsoft.cern.ch or mirror.nsc.liu (the third mirror, archive.kernel.org, listed as an official at vault.centos.org, is not suitable as it upgrades ...