Why are True humans still viable?

True Humans also know as Pure humans are simply easier to train in various aspects quicker with out the potential lost of ones own natural ability.
Super Humans schooling and training, primary focus is on their natural Strength, their organization doesn't need them for any thing else that a normal human couldn't do essentially it would be a waste. Though there is  nothing stopping them from being scholars is the system. The Super Human Gene just locks one down to that specific arch type. Super Humans can not become Formers, or get muscle cybernetics. having this gene also conflicts and prevents Mancer gene from forming, while Contracted are chosen.
Formers, Give up the ability to reproduce unless it is with a Former spliced with a similar gene. I.E Canine with Canine. This only overrides previous genes. Mancers can become Formers but lose their powers. While Superhumans cannot be spliced at all. Cybernetic enhancements are possible, but rare as the usefulness is somewhat diminished in certain areas. (I.E Why splice Cat eyes to see in the dark then get cyber eyes) and extensive cybernetics are flat out rejected by the Former body. Contracted are again chosen.
Mancers. the Mancer requires their flesh to channel there power. any lost of flesh is a determent. Cannot splice and take years to properly train. Cannot become a contracted as spirits fear being consumed by there willpower.
Dolls can not be contracted and  have invasive cybernetics etc.
Enhanced- Cybernetics Trading Biological weakness for technological weakness.
Contracted- have to make a contact with a spiritual partner to utilize their power then using their own bodies to channel this power and turn it into something. Though cybernetics effect Contracted less then Mancers they still need flesh to channel this energy primarily the core and spine can not be changed as per mancers. They have to learn all their skills as well through study.