Hi,
Unfortunately, there is no possible way to download logs through CLI as it will have to save a bunch of data into the router's free space, what could be not enough.
Most of the logs or databases are in .db file extensions and would need to be imported through some kind of other database apps, but I believe logread command output should be enough for you if you're looking for debugging information. To export it into file use logread > /usr/file.txt or something similar to your needs.
So if you wish to download all the configs and logs, the best way to do it - is through WebUI.
EB.