@Fix Right, but it seems body cultivation is discriminated against so it's likely that it doesn't have the resources nor the history to have been as fully explored as those other two have. Therefore it stands to reason that cultivating it first until you've at least built a family might actually improve your overall power even if you later decide to go the gene grafting route or even the cyborg route.
Even if there are 5 tiers of power, you have to assume that 90% or more people are stuck in the 1st tier anyway. If it's a choice between body cultivation which allows you to keep your fertility as well as increasing your lifespan or become half-robot or splicing supicious DNA into your body, I can imagine that most people would prefer body cultivation even if it didn't promise top power and even for those chasing top power might want to try it first.
Even if there are 5 tiers of power, you have to assume that 90% or more people are stuck in the 1st tier anyway. If it's a choice between body cultivation which allows you to keep your fertility as well as increasing your lifespan or become half-robot or splicing supicious DNA into your body, I can imagine that most people would prefer body cultivation even if it didn't promise top power and even for those chasing top power might want to try it first.