The reason we have FastDL in Source Engine is because downloading directly from the game server is slow. FastDL allows you to change where the server's custom content is downloaded from. This of course means you need to put the custom content in the other server.
Blockland servers are probably slow at this too since the servers have other things to manage, like players who spawned doing stuff, and lots of other things. I think Blockland servers should be able to specify a different download location which can speed up add-on downloads greatly.