Unless someone was able to notice they had potential and were willing to take the risk to entrust such a weapon to them, they would struggle to do anything beyond handling lower-grade Spirits.
In most cases, such people who possessed such special physiques were much better suited to dealing with Balancers and ordinary humans rather than Spirits so they would at times be made into guards or even assassins.
It was the same when it came to the method that Ash had discarded but had left for him to make use of.
The method was quite similar to creating someone with superhuman physical capabilities but it came with the same flaws and it did not provide an immediate effect.
It was the type of method that would gradually grant changes to the body each time that a Spirit was killed.