I just got a new computer and installed UE4 from source for the first time. However I have also had to install a launcher binary version of UE4 merely because the launcher offers no way for me to download my marketplace engine plugins or project plugins to my source-built engine or projects.
The launcher should be a hub, not a bottleneck!
Also, the launcher doesn’t actually display your purchased marketplace assets until you find them on the marketplace Vault section of the website. That took me a good frustrating hour to figure that out. Very bad!