What was the Barbarianism or exploitation in which these warriors were engaged? We know that Parashuram’s forces were FIGHTING TO KILL the enemy forces, and NOT just to defeat them. They were however sparing those Ksatriyas who were legitimately getting married to females whom they have kept. That certainly means that there was serious exploitation of females.
People who had developed the habit of eating HUMAN FLESH, and were termed RAKSHAS during passage through sea, formed separate settlements, as others were apprehensive about their behavior.
What is the quantum of Adharm for Lord Vishnu to incarnate is not decided by us earthlings. It is decided by Lord himself. However we need not doubt the fairness of God regarding His presence on earth as Avatar. the quantum of Adarm required for lord to come as avatar would be the same for all ages, yugs and for all humanity.
During the last 1000 years of invaders rule extreme atrocities were committed on Hindus. Without getting emotional, all I can say is that the abuse of females was indescribable. Females, able bodied males and even children were taken away as slaves to their native country. Temples were razed and plundered. Conversion was forced. As I said, I can be only miser in describing all this.
The other was the exploitation of females in which religion was also used. Parashuram father asked his sons to kill their mother for a flimsy reason of her watching some sport, and Gautam Rishi killed his wife Ahaliya, are examples of same. The avatar as Parashuram only tried to make sure that Vaanars were left alone by kingdoms.
(a) Settlement of Vaanars as Humans and
(b) To abolish Agni Pariksha, and establish it as an Adharm plus
(c) Give a message to the future world that Sanatan Dharm believes in EVOLUTION and NOT in CREATION by Establish Ram Rajya. This Ram Rajya did not last long which in itself is a proof that Evolution is important.