Oh I think you and I are gonna have fun.
Do you remember Gear 2 and gear 3? Those are foreshadowings.
Do you remember Shanks stealing the fruit in chapter 1 ? This is a foreshadowing
Do you remember the Nika conversation ? This is a foreshadowing
Do you remember the joy boy conversation in Fishmen island ? This is a foreshadowing.
No, foreshadowing doesn't necessarally mean a story is good. But its one of the best indication it is. The gear 5 is one of the best plot twist of the entiere serie. But the thing you forget is that its not only good because of the foreshadowing, its also the best because of everything else:
- Gear 5 push the theme of freedom to its limits which is the core theme of One Piece but also Luffy
- Gear 5 extend the lore around the One Piece, making its appearance a HUGE worldbuilding moment, not just a cool transformation
- Gear 5 put the spectator on his head by twisting not only a transformation but the ENTIRE story on its head by the fact that something like the gomu gomu fruit it reput into question. This is something only prodigies stories are able to do. So needless to say that it doesn't happen often, even Shakespear had hard time doing that.
- Gear 5 extend the symbolism present in One Piece around the theme of the sun, the down and the moon. Which create an echo chamùber of theme that resonnate all over the story. This is again, something only the best stories can do.
Now for the comparison:
- Supersayan was foreshadow one time (meaning with the same principle "someone saying that the ultimate warrior exist")
- Supersayan is like a lot of story a product of anger. This is not only basic but also very problematic as it portray the idea that when you are angry you can developp a super power. This is a product of toxic masculinity that men face all around the world in media, meaning that in media character are expected to be hero when they are angry and smashing stuff, when in reality, this is the behavior of a violent person.
- While supersayan is cool, it doesn't resonnate in any symbolic way shape or form
- While supersayan is cool, it doesn't turn the story on its head
- While supersayan is cool, it doesn't push forward the world building or the knowledge we have of the fantasy world of Dragon ball.
So yeah
This is not even a match. Not only gear 5 benefit of a bigger hype, gear 5 is also better both in storytelling and symbolism.
Oh and one last thing: Gear 5 is created in such a manner that it transcend the format. By creating a transformation that reminds us of the toons, gear 5 pushes the manga format to its limits breaking the barrier of what is possible in one's story.