So you think if one person is ever in a position of authority over another and those two subsequently end up in a romantic pairing, any number of years after that imbalanced power dynamic no longer exists, it's automatically grooming?
Do you have any dialogue examples that Byleth was grooming his or her future partner during part 1? I'd love to hear those. There are certainly people who analyze every word of dialogue more thoroughly than I'd ever think to, so by all means, if you have any I'd love to ponder them.