The Wikibase image takes a JOBRUNNER_MAX_JOBS setting for use in running JobRunner. When no value is provided from the user it defaults to 2 in the image.
Research and/or test to confirm whether this is the best general JOBRUNNER_MAX_JOBS setting, and update to a better default if there is one.
I suspect that a higher number may be a better default (5 or 10?), but in preliminary research haven't came up with a clear recommendation.