Was the American Revolution a radical revolution?
Not at all.
However, this answer is dependent upon your definition of a "radical revolution." As compared to the French Revolution which happened just a few years later, it would not be described as "radical" but pretty much what you would expect of a revolution at the time.
The word radical means "extreme, drastic or sweeping." In contrast, many Americans at the beginning of hostilities in April 1775 considered this more of a civil war. People had long been looking for a change in the political landscape of American society. Their desire was to be either treated as all people in England were treated or be allowed to form our own country. England, of course, rejected both proposals and the result was in fact a war against the civil political system that existed in 1775 America.
The word "revolution" means an abrupt seizure of power. In the case of America, the American political leaders were looking to take back the power they previous had. That is, King George and the English Parliament had replaced elected American Governors with British Military Governors. England had also replaced many of the courts with judges of its own picking. And so where government was concerned, Americans were seeking a return to what they had had on 5 years prior. But in the process, and where the revolution comes from, is the fact that in the end, through the 1776 Declaration of Independence, we became autonomous.