The Book of Jonah presents no problems for me. I'm not out looking for an ancient or modern fish capable of swallowing a man. I'm not concerned with whether or not anyone believes that a person could survive for three days in the stomach of a fish. I'm not even concerned about the dynamics of when and by whom the story was written.
1) God is more concerned with the well-being of those whom I consider national enemies than He is with my discomfort over my enemies comfort
2) God uses people who have huge flaws to accomplish His 'perfect will'
3) God is patient, but persistent
4) Who God considers to be His children is quite different from the insistence of nationalistic voices past and present
Jonah was reluctant. He was in turmoil over the possibility that the mortal enemies of his people might repent and receive favor from God - his God!
He was reluctant. He was rebellious. He was disobedient. But, most of all, he was called and anointed to accomplish a task. Ultimately he obeyed.
The rest is the story of legends.
Parenthetically, Nineveh was a city with historical record. It ultimately was destroyed, but not within the generation of those who repented after hearing Jonah's message of God's redemptive plan.
The repentance and Godliness of previous generations has no direct bearing on God's relationship to me. Nor does the ungodliness of previous generations have anything to do with how God will deal with the repentance of those we choose to call our enemies.
Unlike us and our nations, God is NOT a respecter of 'persons.'