Short version: Spin isn't just the equivalent of Hamon in SBR universe, it IS Hamon, except it is manifested differently due to a lack of need for ancient humans to develop Hamon the way we are familiar with which is the lack of the Stone Masks that can turn humans into vampires or the Pillar Men race, because in SBR universe, Kars, or the analogue for Kars in SBR universe either did not exist along with the other Pillar Men or that he and his race existed but he was prevented from making the Stone Masks in the first place/he didn't want to make such a thing to begin with/his race never made contact with humans for some reason.
Long version: So, with Araki having completely moved on from vampires by continuing the story in an alternate universe that has no real connection with Part 1 to 6 other than characters that share familiar/similar names and/or history of pre-SBR characters, it's safe to say that Stone Masks do not exist in SBR universe.
In the world of SBR/Jojolion, vampires and Pillar-men seem to be non-existent as well. Either that or the Pillar-Men has been replaced by the Rock Humans shown in Jojolion. Pre-SBR, vampires exist because of the Stone Masks, which was created by Kars, so if there are no Pillar Men/Kars and/or the Stone Masks, It means that there are no vampires in SBR/Jojolion universe, period.
However, this means that without Pillar Men/Vampires, humans would have felt no need to channel sun's energy into Hamon because they would've lacked the incentive, that is, the survival need to develop such an ability. STILL, it doesn't mean that they didn't have the potential to harness it in some form, some individuals do possess this capability, one of them being the Zeppeli family.
The Zeppeli family is known to have created the Spin in the first place, so in a universe where there are no vampires or Pillar Men, Hamon is developed the way we see it in Part 7, so instead of the power to channel the sun's power through breathing, it's the power to control some sort of supernatural rotational force that can manipulate the body in such a way that resembles Hamon and more.
So to sum it up: Due to the non-existence of either the Pillar Men, Kars, Kars' Stone Masks, Vampires or all of the aforementioned things, Hamon as what is shown in Part 1, 2 and 3 never came to being, and the Spin is a form of Hamon that came to being due to humans having no need to wield such a power to defend themselves from creatures like Pillar Men and Vampires.