"The main issue in King Lear, is the abuse of power. Everything else is subordinate to this theme."
Who made that statement? Since you are basing your essay on it (or, rather, on the refutation of it), you need to at least acknowledge who said it. Also, you need to be more clear about your thesis in your introduction, stating clearly that you agree that abuse of power is an important theme in the play, but that you believe that other themes are of equivalent or greater importance.
It's not enough, in the body of your essay, just to show that other themes exist. The statement you are refuting does not deny that other themes exist but, rather, states that all other themes are subordinate to the theme of the abuse of power. So, if you think that reconciliation or blindness are of equivalent or greater importance than the theme of abuse of power, you need to cite some evidence to support that belief.