I enjoy each generation having its own central figures being developed variations of the previous generation's themes. Atm we are seeing the strongest example of tobirama's theme that danzo developed after eschewing the "silver lining" that tobirama posessed. Im still aware and asserting that danzo was way more an a** hole than tobirama and several degrees more aware of the darkness and negativity his actions would foster. Hewas totally into it! Tobirama had hashirama rub off on him a little and when making up his own mind; was arriving at answers that were as of then still untested yet formed with a pinch of noble sentiment of solving war and atrocity.
I get the impression that the pre-village era was of many powerful shinobi and powerful ninja were more common. With uchiha running in gangs with multiple sharingan users.. it makes me think that the village era was to slowly remove the power from humanity as each country weakened considerably after every war (most cases) hashirama would likely have had a vision of diminishing jutsu so ppl could calm down and stop killing each other's kids. Being born with shinobi powers only guarantees the shinobi affairs and circumstances of a danger and pain filled life. The less shinobi born then the less shinobi die. I can totally see this as a deliberate outcome.