Note: this question is inspired by this answer.
Some cite Hebrews 1:1-3 to argue that Jesus Christ was the ultimate special revelation from God, and that the office of prophet was thus rendered unnecessary as no further revelations would be required:
Long ago, at many times and in many ways, God spoke to our fathers by the prophets, 2 but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world. 3 He is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. After making purification for sins, he sat down at the right hand of the Majesty on high, (Hebrews 1:1-3 ESV)
However, Acts 21:8-11 refers to the gift of prophecy and prophets as if they were normative and still in operation in the early church, in circumstances where Jesus Christ had already been revealed and already ascended to heaven.
8 On the next day we departed and came to Caesarea, and we entered the house of Philip the evangelist, who was one of the seven, and stayed with him. 9 He had four unmarried daughters, who prophesied. 10 While we were staying for many days, a prophet named Agabus came down from Judea. 11 And coming to us, he took Paul's belt and bound his own feet and hands and said, “Thus says the Holy Spirit, ‘This is how the Jews at Jerusalem will bind the man who owns this belt and deliver him into the hands of the Gentiles.’” (Acts 21:8-11 ESV)
Is there a contradiction between Hebrews 1:1-3 and Acts 21:8-11? How could Agabus and Philip's daughters still be prophesying if Jesus was the ultimate special revelation, rendering all further special revelations unnecessary (that is, if we give the benefit of the doubt to arguments such as this one)?