"Destiny" is nothing more than knowing the future and seeing how things turned out. If someone "has" to be there for an important event, it's not because it was preordained by some cosmic force; it's just because they happened to be in the right place at the right time for that particular timeline to turn out in a positive way. That's what happened here. In the original timeline, Janeway happened to be in the right place at the right time to make the key difference. When "Endgame" altered that history, it led to a timeline in which Janeway wouldn't be there to make that key difference, so Q Junior had to correct that.
I think that Beyer's book disagrees with you. There is a very strong vibe throughout the whole book that there is something moving the universe. I mean, Janeway even becomes aware of her own soul,
They have always been there, underpinning what she believed were more useful to her: reason and passion. But, however briefly, Kathryn had touched something infinitely deeper. That short exposure had left her adrift but more firmly anchored to herself.
She had never shared with anyone the absolute devastation she had felt when a scientific explanation had been discovered to explain the ‘miracle.’ Had she spent more time in the company of her soul prior to this experience, the would not have been as quick to return to business as usual. Kathryn did not need to locate her soul within her. This ineffable thing was now the sum total of her reality”
So it certainly seems that there is more to the universe than even the Q know, since their immortality gives them no ability to know what lies beyond death for the soul.
"I know," Q offered, "but surely you are beginning to sense that as you exist now, there are many options available to you that were not when you were alive." Kathryn knew the truth of his words. But she did not understand how the tenuous connection she now felt to both the living universe and the exponentially greater power that still beckoned to her from beyond it would give her any power that could rival a Q.
There is something big out there even beyond the Q and that power, after reading this book twice seems to be destiny (whatever that means, since Beyer does not explain, just leaves it open to the reader to interpret.)
This idea is all throughout ST '09. These people, no matter what happens to the timeline are destined to be together, on a ship called Enterprise. This book is rife with the idea that people are in places at certain times for a reason. DS9, Sisko is created just to save Bajor, and now Junior and Eden have been created to heal a rift in the universe. Something is behind and the multiverse is not as random as we thought.
Now I am sure you will disagree. But I see this tread running through this entire book and found it really cool that Beyer would go there. Spock tells Valaris that she should have faith that the universe will unfold as it should. It seems that there are forces at work to bring about good in the universe and at work for balance. Faith, this is what Janeway is learning in this book, that there is something infinitely bigger out there than just science and reason and it starts with the soul.