Does deleting an original asset but keeping the transform folder asset make Craft replace the original file with the biggest transform?
Does deleting an original asset but keeping the transform folder asset make Craft replace the original file with the biggest transform?

No - Craft will always use the originally uploaded asset as the &quot;source of truth&quot; for generating new transforms.
You can, however, replace the originally uploaded 8mb+ file with a smaller one, and it'll be used as the source of truth for generating new transforms.