It cannot be assumed that equity was following common law whenever they agreed, any more than the converse.
Our lady the Common Law is a very wise old lady though she still has something to learn in telling what she knows.
Not that pleading can be taken as a test, for the forms of action, notably Debt, ignore the fundamental difference between duties imposed by law and duties created by the will of the parties.
Consider the Essay as a political pamphlet on the Revolution side, and the fact that it was the Whig gospel for a century, and you will see its working merit.