This is Sunny’s greatest strength, and had been of great help to her in her encounter with Opaline, as she does not consider herself a leader - which the writers in MYM may have gone too extreme on by letting her become too inactive , but in TYT we see that she acts more like a leader for her friends and others in times of need. For her, alicorn powers are for helping, not ruling, and that means her destiny is that she will one day become a princess - not by ruling, but by setting an example to inspire everyone with friendship, unity and hope. She doesn’t need power to become a princess.
What makes it easier for Sunny is that the alicorns may have become mythical figures for the G5 ponies which means that they have forgotten the importance of the alicorns - magical super beings - and therefore they do not know why it was natural for ponies to submit to the alicorns . We saw that ponies still can’t ignore their instincts when they meet real alicorns, which makes them respect them - or fear them, recognizing their strength. Ponies are herd animals, which instinctively seek out the strongest who are designated as leaders. So far we see that the G5 ponies do not understand their instincts.
By focusing on helping, and then just being available, Sunny gives ponies the freedom to choose for themselves what they want, the last thing she wants to do is push them. The G4 ponies lived in a dangerous world with magical supervillains, dangerous magic, monsters and hostile powers which means that these must therefore have the alicorns as leaders in such a world. This world does not exist in G5. We haven’t seen a single monster so far - which has completely disappeared, one of the biggest unanswered mysteries of G5. For Sunny, that means she could help out in a much peaceful world, with the clear exception of Opaline who proved the thesis that only an alicorn can stop an alicorn.
It is possible that the moment Sunny gets the princess title will be when G5 ends, because she will have resurrected the tradition, but in her own way. TYT episodes about Sunny and her parents showed us that there are secrets that are yet to be revealed.
Let’s see how alicorns arise; it happens with two methods; ascension and birth. Twilight became an alicorn not only for her magical feats, but also for her actions as part of the Mane 6 and even before she was born, her fate was predetermined. Fluffy Heart was born to an alicorn mother, which proved that the alicorn powers could be genetic, but it could be because Cadence’s magical talent was particularly strong. In all known cases, alicorns were foretold as if their fates were sealed - which means that magic, the ponies’ collective magic, is essential to would-be alicorns.
It could mean that Sunny, like Twilight, was born to become an alicorn, and that even as a filly she had the ability to ascend and become an alicorn. We’ve seen that other ponies with a clear exception like Cozy Glow whose background is a mystery, don’t become alicorns through an overdose of magic - Pinkie at the end of G4 was the best example, these have to be “accepted” by the mysterious magic.
So Sunny’s fate is already decided from the beginning, especially by being the Element of Hope.