All Avatars come from the same Divine Source. In this sense they are one. But there is a difference in manifestation hence we cannot say that they are same. An Avatara is not a repetition of the previous Avatara. Isn’t it evident in the parable of the Avatars itself? The knowledge and the power that the Avatar brings, the work and mission he is here to accomplish, the Age and the context, the stage of human evolution and outer development etc determine the nature of the Divine manifestation and condition his action. Only that much of the Divine Force is expressed in the life of the Avatar as is necessary for his times. The rest of the divinity is held back and veiled.
Sri Rama came amidst an animal and asuric humanity and hence he embodied a luminous sattwic nature. Sri Krishna born amidst a half titanic, half human mankind struggling towards the full human type embodied the superhuman to help humanity free itself from bondage to ignorance and be liberated through works. Sri Aurobindo comes when humanity has arrived at the utmost peak it is capable of through the mental evolution assisted by the gods. The evolution of man initiated by Sri Rama, carried forward by the Buddha and Sri Krishna has arrived at its culmination now. If pressed further it will move in endless circles of increasing technology or else slide down unable to respond to the evolutionary pressure to go further. Sri Aurobindo has come to assist the fully developed mentalised humanity into the divine superhumanity of the future. That is where the difference lies.
Affectionately,
Alok Da