When grouping by Epics on the next-gen board, there is no way to reorder the Epics. This makes it impossible for the dev teams to know which is the 'next Epic off the rank' when picking up new work.
If you could sort the Epics on the board, that would solve the problem.
Ideally, there would be some link between the Roadmap and the Jira board. However, there are cases where roadmaps overlap, making the Epic sequencing unclear. Hence, the primary ask here is to allow the Epics to be at least manually movable on the Jira board.