dear Terry...
The gospel of john was a personal account of Jesus...the revelation to john is was he was told to write as he was seeing it in a vision. The revelation is a book that portrays the final battle between good and evil. The harshness expressed in it is to be expected for such an epic battle.
We are faced with the vision of two "camps": God's and satans. Until satan and his angels are cast to earth they are still heavenly principalities.(Ephesians 6:12) Once they are cast to the earth there is even more woe to the earth and to the sea. What is described as vindictive is Jesus ridding the earth of those who are in opposition to His righteous reign. Jesus literally supports PEOPLE (rev 6:10) who have been slaughtered by those who are in opposition to His righteous reign. The tribulation is satanic/demonic it is initiated against "good". The wrath of God is initiated against "evil".
As far as the dating of the book of revelation, in the following link mark hitchcock presents external evidence for an AD 95 date based on EARLY written testimony refering to the time and event of the revelation when john was on the island of patmos. that testimony refers to john being on the island during the reign of emperor domician. @ 24-26 minute mark.
https://m.youtube.com/watch?v=b6FOx_4wujg
love michelle