Bob P, I take issue with your post. (wry grin)

Seriously though, I would define a "major protest songwriter" as a writer who:

1) Has written several songs with large elements of "protest" and social justice in them,
or
2) Has written at least one song that has had a major impact on the way I or others think about issues of social justice.

Or both.

Songs with just some elements of protest don't count as "major" in my opinion.