Mishloach manos and, especially, matanos laevyonim reinforce the need for Jews to assist their friends and, especially, the disadvantaged. The Arizal maintains that the unity of Yom Kippur exists in an unnatural state. In the absence of work and physical pleasure, Jewish unity is more readily achieved. As such, it is hardly a precedent for the rest of the year. In this sense, Purim is greater than Yom Kippur.
Work is permitted and eating and drinking are mandatory.
Unity under such circumstances is a greater accomplishment and a better example for other days as well. Purim and Yom Kippur share another common factor. They are both days of kabbalas haTorah . This is no coincidence. The Torah can be given only when there is Jewish unity.