ability to refer to attributes of sub-task Parent (JIRA-Cloud)

I know this has been raised in other tickets, but they seem to refer to server installs, not Cloud.

I have a board showing sub-tasks in swimlanes by their story. Story is "Team A" or "Team B". I want to be able to make a quick-filter to show only Stories (and their sub-tasks) for Team A or B, however if I use
"Assigned Team" = "Team A"
then the sub-tasks don't show as they don't have "Assigned Team". If I try something like
"Assigned Team" = "Team A" or issuetype in subTaskIssueTypes()
then all stories (Team A or B) with any subtasks show up as swimlanes, when I only want to see the stories with Team A (and their subtasks)

If sub-queries are a no-go for some reason in Cloud, then please propose how this can be done
I want to really do something like
"Assigned Team" = "Team A" or (issuetype in subTaskIssueTypes() AND "parent.Assigned Team" = "Team A")
or
"Assigned Team" = "Team A" or (issuetype in subTaskIssueTypes() AND parent("Assigned Team") = "Team A")

For now we've added a post-function on sub-task Create Transition to set the sub-task Team value from the parent, but if the parent Team is changed, then the sub-tasks don't get updated.

This sub-query, or parent-attribute capability is essential to make these boards useful for our teams.

I suspect a similar ability to refer to the attributes of an issue's Epic-link would also be of value (again, sub-query or other more limited approach).