You raise an interesting point. Does the subversive writer need to be a radical writer? I would say no. Radical writers are surely mostly subversive, but the inverse is not necessarily so. Subversive writers are not always radical.
Subversion can be more subtle and slow. It may seek to influence, and this can be accomplished by questioning or destabilizing a norm. Radicalism is more overt, more intense, more revolutionary, in calling for radical change.
It may be said that Dickens was calling for change, not only in social conditions by highlighting them, but especially in individual hearts, in his subtle way. This is certainly apparent in A Christmas Carol with the transformation Scrooge undergoes -
“I will honour Christmas in my heart, and try to keep it all the year. I will live in the Past, the Present, and the Future. The Spirits of all Three shall strive within me. I will not shut out the lessons that they teach.”
And remember Marley's speech -
“Mankind was my business. The common welfare was my business; charity, mercy, forbearance, benevolence, were all my business. The dealings of my trade were but a drop of water in the comprehensive ocean of my business!”
And in Great Expectations -
“That was a memorable day to me, for it made great changes in me. But it is the same with any life. Imagine one selected day struck out of it, and think how different its course would have been. Pause you who read this, and think for a moment of the long chain of iron or gold, of thorns or flowers, that would never have bound you, but for the formation of the first link on one memorable day.”
And in David Copperfield -
“Whether I shall turn out to be the hero of my own life, or whether that station will be held by anybody else, these pages must show.”
And in A Tale of Two Cities -
“Death may beget life, but oppression can beget nothing other than itself.”
And a quote from Dickens outside of his writing -
“The most important thing in life is to stop saying 'I wish' and start saying 'I will.' Consider nothing impossible, then treat possibilities as probabilities.”
Taken in the context of the themes of his writing, I would call that last quote a call to action.