Correcting balance is a possible motivation
Yes, and let's explore that. Consider the True Neutral Druid who came to the worldwound and was turned into the protagonist. The sort of person whose motivation would be based around the capacity to erradicate the worldwound and restore Sarkoris. Like every other main character the Druid will receive the same first impressions as everybody else. They'll get the light of heaven. They'll feel the impulses of the abyss. They'll interact with the Aeon soul. And so on. One of which is very likely to make a lasting impression: being transported to Elysium, interacting with it's unbridled wilderness and speaking to the Azata, outsiders who are themselves connected to natural and elemental powers. That druid might make the choice of becoming Azata themselves. Sure, they'll turn Neutral Good along the way, but that's just it: character development. One might even call it
[an] exploration of what it means to live in a world where morality can literally be in your blood and is a metaphysical property of the universe.
Likewise, that same Druid might see in the Aeon's intentions the true power needed to restore Sarkoris: in casting a spell capable of changing the timeline, one averts the worldwound entirely and saves millions. Yet in becoming an Aeon, they will turn Lawful Neutral along the way, as well losing their humanity in the process.
Also a true neutral/flavourless path
Ah, but that was never on the table, was it? The Legend path is not the flavourless path. Far from it. It is integral to the story of the Legend that they spent the last few weeks slowly ascending into an outsider power. Going back to our Druid friend, they have just realized that their soul was part of an experiment. That it was made to resonate with the powers that be. That they are being slowly overwritten into a separate being, neither Areelu's child nor themselves, but a demigod with traces of both and so much more. Their reaction might be enthusiastic. Or they might realize that their choice in becoming an Aeon or an Azata was not a sober one. The rejection of your mythic powers could be the moment where the Druid's humanity shines through, dispelling the Aeon's alien mind. Or maybe they think that while Elysium is the promised land, nature must be reborn by mortal hands and mortal efforts. Their personality restored, they'll now spend the remainder of the game, and the post game, either working back to their original alignment of True Neutral or partially embracing the new perspectives that their stint as an outsider gave them in life.
while being unrestricted by the choice of the other 6 very flavourful mythic paths.
I can sympathize if you didn't jive with any of the early mythic paths and would rather be Legend from the get go. I have a similar issue where I sympathize the most with the Trickster mythic while disliking it's associated mechanics a lot. I've spent a long time trying to accomodate Trickster's powers with the sort of character I tend to play with and the results are not great. But tought luck, right? Story and gameplay aren't divorced from each other, if I want to play a Trickster I'm gonna have to play with it's powers. There never is such a thing as unrestricted roleplaying in a CRPG. Substituting the reality of the game world with something else entirely is never a satisfying option.
That said my advice is to work with what the game already has. A lot of people went into the game really hyped for the Late paths, like Devil. And lot of people left unsatisfied because Owlcat games tend to lose steam on the fourth act onwards and of course there isn't Angel-tier Devil reactivity crammed into the final chapter of the game. However if you look at the full story of the Devil as one that uses their past stint as Azata/Aeon, then it becomes much more reasonable and interesting as an experience. Even if it is also very much fair to say that the Late game paths desperately need more content. Looking at you, Gold Dragon. Likewise, while Legend is the non-aligned path it is not the flavourless path. It is not the unrestricted roleplaying path. It is something *much better*. It is the path where the Hero gets closest to their most idealized outsider power and, for some reason, rejects them in the end. That is true roleplay gold. It is akin to playing a Hagbound Witch in PnP and going through all the story beats required to reject the Hag's curse. It's what the kids call pure kinomatography.