Who decides which caste is SC, ST and OBC - President or Parliament?

This is what Article 341, 342 and 342A have to say:

341. Scheduled Castes.—(1) The President [may with respect to any State [or Union territory], and where it is a State, after consultation with the Governor thereof,] by public notification, specify the castes, races or tribes or parts of or groups within castes, races or tribes which shall for the purposes of this Constitution be deemed to be Scheduled Castes in relation to that State8[or Union territory, as the case may be.]

(2) Parliament may by law include in or exclude from the list of Scheduled Castes specified in a notification issued under clause (1) any caste, race or tribe or part of or group within any caste, race or tribe, but save as aforesaid a notification issued under the said clause shall not be varied by any subsequent notification.

342. Scheduled Tribes.—(1) The President 9[may with respect to any State or Union territory, and where it is a State, after consultation with the Governor 2 thereof,] by public notification, specify the tribes or tribal communities or parts of or groups within tribes or tribal communities which shall for the purposes of this Constitution be deemed to be Scheduled Tribes in relation to that State or Union territory, as the case may be.

(2) Parliament may by law include in or exclude from the list of Scheduled Tribes specified in a notification issued under clause (1) any tribe or tribal community or part of or group within any tribe or tribal community, but save as aforesaid a notification issued under the said clause shall not be varied by any subsequent notification.

342A. Socially and educationally backward classes.—(1) The President may with respect to any State or Union territory, and where it is a State, after consultation with the Governor thereof, by public notification, specify the socially and educationally backward classes which shall for the purposes of this Constitution be deemed to be socially and educationally backward classes in relation to that State or Union territory, as the case may be.

(2) Parliament may by law include in or exclude from the Central List of socially and educationally backward classes specified in a notification issued under clause (1) any socially and educationally backward class, but save as aforesaid a notification issued under the said clause shall not be varied by any subsequent notification.]

The wording makes it a bit confusing - If President releases the list then he is deciding, but if Parliament has the authority to modify, then Parliament is deciding.

Just two more:What was the need to include President in this?The Parliament could have directly released a list.

Can we say that it is a discretionary power of President and Governor?(I accept that he releases the list in consultation with the Governor of concerned state and that it can be modified by the Parliament, but given thatHE is the FIRST ONE TO RELEASE THE LIST, can't we say that he is using some discretion here along with the Governor? After all, even if the Parliament, in a hypothetical case, rejects all his suggestions, atleast we can say that the Prez tried to do something)