I agree, the defaults have been pretty dumb for a while but disabling one of the log types does affect those users who expects the one they use to work. I think a better option would be to get rid of both syslog and maxlog parameters and introduce a new one called log_type which would be a multi-valued enumeration that allows you to select which sources the log messages are written into. Regardless of what we do, we'll have to pick a default log source. For non-docker setups I believe the systemd journal would be the better option as it provides a more structured way of storing information with log messages.
For the short term, I think we could fix the problem by disabling syslog if MaxScale knowns the systemd-journald isn't up. This would mean the log output in the GUI would default to the file-based logging in docker containers.
As for the docker images, this is a known problem and it's tracked in MXS-3457.
By default logs go to both syslog and maxlog as they are both enabled by default. Is this in a container environment or is there some other reason why syslog (or journald to be more specific) doesn't contain the messages?