Hmm very interesting question. However, I do not think there is simply one hero of Arda. I believe, that there’s a bit of a hero in everyone. Not all did necessarily great deeds, but it all contributed to the greater domino effect of the events lining up. From Merry and Pippin making plans to move Frodo to Buckland all the way to Eärendil bringing down Ancalagon the Black.
So yes, everyone is a hero in their own way. If Luthien and Beren hadn’t fallen in love, we wouldn’t have the characters we love today. And yes, bold of me to say but, if Fëanor hadn’t made the Silmarils, all essence of the Trees would have been lost. If Maedhros hadn’t been Maedhros he wouldn’t of sprung back from his captivity and led the March of Maedhros. If Aragorn would have had a lust for power as lesser men, and should he have taken the throne before his due time, Gondor would have fallen. Had not Bilbo told Gollum his name, all would have been different.
So after all, every individual contributed to the end piece, even if it took them a step away from it at the moment. Looking back at the big picture, it all came together eventually. In the end, there’s a hero in all of us and that, I think, was exactly one of Tolkien’s points.