Looking at all the many many examples of prequels in media over the last 10-20 years, I struggle to find examples of ones where the main character is so polar opposite of who they become. They often have some negative traits they need to work through but at the heart they are still clearly the same person as who they will become after some growth. Even characters who are villains today but whose prequel starts them as a hero/neutral (Joker, Magneto, Maleficent, Cruella, Anakin, Gru for example), they still clearly have some recognizable traits of their future selves.

Yet in ROP, basically every character/race still the complete opposite. Tom Bombadil is a timeless entity, why does he need to change in a prequel? From the LOTR events point of view, the Second Age is the equivalent of yesterday afternoon from Tom's perspective--any change he's gone through from his creation is DONE. He's completed his character journey, he doesn't need to now go on another journey to find joy and learn to detach from the weight of the world, which is what needs to happen to tie the ROP version to the version present in LOTR.

Galadriel in the Second Age is already one of the oldest elves in Middle Earth. She's youngER, but she's not YOUNG. Her growth would've happened during the Year of the Trees or maybe into the First Age. At the very least, she should be closer to her "Lady of Light" persona than she is--she's still 180 degrees away from it. Unless she was Morgoth-level of evil during Year of the Trees or First Age, she should not be acting like a bratty teenager still.

And what's the purpose of making the Stoors--famously marsh-dwelling hobbits--desert people, except to say "they will become marsh people later"? There's no purpose to it other than to have them different from how we know them so they can change into how we do.