I can see where you’re coming from, but there is also another significant difference between a repeater and an flex field. Each row of a flex field can have completely different sub fields where a repeater always has exactly the same sub fields. For me this is the important deciding distinction/factor when deciding whether to use a repeater or a flex field.
Also, repeater fields can be collapsed and if you’re going to have enough rows in the repeater to need to scroll and drag when collapsed your going to have just as many collapsed flex fields rows to deal with and still need to scroll while dragging.
At any rate, if you want to get this suggestion to the developer then you should open an support ticket here https://support.advancedcustomfields.com/new-ticket/
