We should interpret this to mean that the length of the article is commensurate with the importance of the branch in the Framers’ eyes. The Framers clearly meant to have the legislative branch be the most important, with the executive next and the judicial last.
The Framers did not want a very strong president. They did not want to risk having another king. They felt that the Congress was the branch that was most representative of the people and that it should have the most power. This is why they paid so much attention to Congress and its powers in Article I. This attitude towards presidential power was largely accepted by Congress and by presidents for most of the first century after the Constitution was ratified. Presidents generally deferred to Congress during that time.
The Framers also felt that the judicial branch would be the least important. It would not have the power to legislate or the power to carry out the laws. Alexander Hamilton described it as the “least dangerous branch” of the government. He felt that it, unlike the other branches, would be unlikely to infringe upon anyone’s rights.
Thus, we should take the lengths of the articles as a hint about the degree of power that the Framers wanted each branch to have.