Last resort logger works only if no handlers are set.
NullHandler for example is used on most libraries in order to prevent setting up the logging system, but it can cause errors not to show.
Also, LastResort is set for the "Warning" level. -L<level> will give you the flexibility you need in order to debug issues.
Theoretically you can solve it by -L ignoring null handlers and setting last resort handler to the given level, but that's too magicky. I believe using basicConfig is the cleanest and most user friendly solution.