It's really simple. The boon for one can be a curse for another is the phrase that comes to mind when Jason and Percy are involved. All the things that Jason deems as boons are akin to a curse for Percy. Things Jason wants and Percy does not want are denied to the former and thrust upon the latter. Destiny is inherently unjust to both of them.
Their lives are quite literally inverse and parallel of each other simultaneously.
Percy was initially hated and ostracized for what he was, while Jason was honored and revered.
Jason became the image everyone forced on him in hopes of finally earning genuine love, respect, and approval but was instead seen as doing what was already expected of him and was rewarded with even more expectations.
Percy who broke all preconceived and hateful notions about him by breaking records and creating miracles that the demigod world did not know existed and cemented himself as someone who would never be forgotten. He paid for all that in blood and pain, but at least he was rewarded with the love and loyalty of his peers for it. [Jason would call this a gift, a reward while Percy considers the price of love, respect, and loyalty of his peers was unjust and should have been given freely]
Percy's name is a gift and a prayer. It's the earnest symbol of Sally's need to keep her son alive and safe. Percy may be a symbol of a god's mistake once up on a time; but he is not a regret. No, he is a blessing in disguise.
Jason's name is a curse and a sacrifice. It is also a symbol of a god's mistake and, more importantly, a god's regret. He himself is a tool, a peace offering, and a sacrifice disguised as a gift. He can never be anything more in the eyes of his makers.
Percy is a symbol of love for both Poseidon and Sally. Jason was a symbol of status to Beryl and a bargaining chip to Jupiter against Hera. Poseidon would go to war with Zeus for Percy's sake while Jupiter would see Jason dead for his own agendas. And he did.
Jason desperately wants to be a legend that was woven around him while Percy wants to escape the legend he became and created.
Even their definitions of freedom are inverted.
To Jason, his freedom is being able to help the gods and his camp in whatever way he can and not be judged for it. His freedom is in the genuine love and respect of his peers and the approval of his father.
To Percy, his freedom is being left alone, without the watchful eye of gods on him, being able to do what he wants, whenever he wants. He cares not for earning the approval of any gods, instead he is the one that judges them to be worthy or unworthy of his respect.
Jason wants to be a leader while Percy is doomed to be one.
But by the end of it Percy is now the one saddled with responsibilities and expectations that he does not want ,drowning and chafing under the weight of such restraints that go against his nature while Jason's death despite it's unjustness has finally freed him from his shackles.
Jason is free, and Percy is not. Jason sees his death as punishment while Percy would think of his own death as freedom even though Jason's death is the actual freedom, while Percy's death would be the true punishment, after all he was so close to escaping his fate.
Their dynamic was perhaps the one with the most potential in the entire series, followed by Percy and Luke. The parallels, the contradictions, the mirrored philosophy, and mindset. All that golden potential and Rick squanders it on a superficial rivalry and poorly fleshed character motivations.
Jason who everyone believed would be great and Percy who knew that everyone except his mom believed he wouldn't amount to anything unless he proved himself. Percy who chose to make the Great Prophecy about him so Nico wouldn't have to bear more burdens after losing his sister. Jason who chose to confront Caligula alone so Piper would live after the oracle told him he or Piper would die.
Percy who believed he would die at 16. Jason actually dying at 16.
Imagine if Percy and Jason actually had the chance to have a genuine conversation about how being sons of The Big 3 hurt them in different but similar ways bc of what was expected of them and bc of how they were treated by people. Percy and Jason knowing that they can't really show weakness or insecurity or ever say that they were scared bc everyone at their respective camps were counting on their leadership.
Percy and Jason who had their own distinct journeys to be the heroes they became and both journeys were valid and important but did Jason and Percy ever believe for a second that they were important not for their parentage and achievements but because of who they are and actively chose to be