"the increasing use of automated and semi-automated edit-review tools has brought about an increase in rejection"
Do we know how the language used within these tools impacts the response from new editors? An automated tool written with language that is friendly and welcoming compared to something that sounds cold or (too) severe might actually impact the response from editors. One potential approach is a non-technical one. Re-write the dialog/interface/messaging of a tool and see if there is any impact to retention of editors who encountered that tool.