With 7.4 version there is an ability to have history access via structure item (history) or via issue.history. But there is also possibility to access worklog wtihout possibility to access issue.worklog, which makes impossible in formula to navigate to worklog of linked issue. I believe that worklogs could be also accessed by issue.worklog

Yes - it is possilbe to make this through structure attributes when you add child issues but it is like creating formula in excel using same column for calculation - doesnt seem reliable.

Thanks in advance! Happy to use such great, useful and advanced product!