I think Bombadil is kind of a goofy character. And I think he is unnecessary for the plot.
But I still like that he's in the book. And I like him because he is unnecessary for the plot. He is one of many elements that Tolkien includes who are there not to advance the story, but flesh out Middle Earth as setting that goes beyond the exigencies of plot. In TTRPG terms, he makes it feel like more of a sandbox and less of a railroad. He reminds the reader that the history of Middle Earth is bigger than the war with Sauron.
So I see Bombadil as a character that violates most of the norms of good writing, but then, Tolkien does that in quite a few other ways, too. I think he is a uniquely Tolkien inclusion, and I think he is an important reason that no one else feels like Tolkien, despite the many, many efforts to emulate him.
As a critic, I find myself almost at a loss in assessing Tolkien. His writing is often expository, his dialogue frequently fails to come across like actual people talking, he includes unnecessary plot elements and characters, his prose is like weird combination of the King James, Beowulf and, I dunno, Tennyson? By most of my usual measure he should be bad, but he's not. It all just works.
For me.
Herbert, not so much. I think only the first book is any good at all, and even then it has some super icky themes and ridiculously unbelievable characters. Basic fantasy plot, with very well executed battles. Cool setting, though, for sure.
Bombadil (and other elements) reminds us of who the actual audience of the book was. The Hobbit, and it's ensuing sequels (the Lord of the Rings) were written for children...or more specifically...Tolkien's Children. It's not supposed to be heavy, it's not supposed to be full of adult ideas (those things that make movies rated 18). They both have elements of fairytales and fairy within them. They are more Harry Potter than Game of Thrones.
They can be dark and scary (much like Doctor Who can be scary...but just enough to scare the kids, not to send them screaming into madness and convulsions...at least generally), as well as violent, but not so violent as to be explicit.
The Silmarillion and other writings were his adult stuff, or his more adult stuff. That was (if I understand correctly) what he really wanted to get published (though I also understand he kept changing and rearranging it as he went along), but the public just wanted more hobbits.
As the books dealing with Hobbits (those little munchkins), and written for his kids, you have such things as a dinner party with an unexpected bunch of dwarves, the humor of how relatives are and how you have to put up with them, the setting up a birthday party, and many other things, one of which is, of course, Tom Bombadil.
This more kid friendly and fairy tale look is where you get things like Hobbits spending time with the Ents, and after horrific experiences with being captured by orcs having almost no PTSD and instead being able to smoke Pipe weed and greet your delayed friends into a flooded siege of a wizard, or how everytime it's the eagles which come to the rescue.
The darkest of the books is probably the Return of the King, showing that darkness leaves it's mark and you still have that fairy tale ending of the Woodsman becoming a King and marrying the Princess and the ones most scarred (the ringbearers) getting to literally go across the ocean with the elves and live in literal middle earth heaven.
Tom Bombadil is just a reminder that this isn't a book written for us adult(such as Game of Thrones was in our modern times), and wasn't Tolkien's first choice to have published. It was written for his children.
If you want what his adult tastes would focus on read the other stuff (The Silmarillion or the newer novels that were printed posthumously), some of which still are relatively light, but there are some rather dark themes and ideas in there that are not really fairytale like.
