Here is a series from Covenanter Reformation showing that the Pope of Rome IS the Man of Sin described in 2 Thessalonians 2.
Part 1 discusses how Antichrist and the Man of Sin are identical: https://covenanterreformation.wordpress.com/2015/04/17/the-pope-the-man-of-sin-part-1/
Part 2 discusses how the Pope fulfills the description in 2 Thessalonians 2: https://covenanterreformation.wordpress.com/2015/04/20/the-pope-the-man-of-sin-part-2/
Part 3 discusses who the “restrainer” is and how Antichrist was to appear after the fall of the Roman Empire: https://covenanterreformation.wordpress.com/2015/05/04/the-pope-the-man-of-sin-part-3/
Here is just one quote from this series showing that historicism is the long-standing interpretation of the believing church:
Cyril of Jerusalem (313 – 386): “But this aforesaid Antichrist is to come when the times of the Roman Empire shall have been fulfilled, and the end of the world is drawing near. There shall rise up together ten kings of the Romans, reigning in different parts perhaps, but all about the same time; and after those an eleventh, the Antichrist, who by his magical craft shall seize upon the Roman power; and of the kings who reigned before him, ‘three he shall humble,’ and the remaining seven he shall keep in subjection to himself.” Catechetical Lectures, section 15, on II Thessalonians 2:4, Nicene and Post-Nicene Fathers, vol. VII