Does the verse, "You may put off whom you will of them, and take to yourself whom you will," mean that the Prophet, may Allah’s prayers and peace be upon him, had the right to choose whom to marry and whom not to marry among his wives, and is there any injustice in this?

Allah Almighty is far removed from injustice. Regarding the verse: (You may postpone [the turn of] whom you will among them and take to yourself whom you will), the exegetes differed concerning its meaning. Some held that it pertains to those who offered themselves to the Prophet, peace and blessings be upon him, while others held that it pertains to his wives regarding the division of their turns. Ibn Jarir combined both interpretations, holding that the wisdom behind this was to gladden their eyes and make them content with what was allotted to them, knowing that the matter was entrusted to the Prophet, peace and blessings be upon him, by Allah Almighty, and that whatever came to them from him was a favor. The Prophet, peace and blessings be upon him, would divide his time among his wives by choice, not by obligation, and this would please them and increase them in honor.