But, the new ribbon interface was much more inconvenient.

If I recall correctly, pasting data while removing duplicates in the ribbon interface was Alt+AQORT, but only Alt+XY in the old Excel (I don't remember what X and Y were, but I know it was a 2 key combo!)

Excel kept the old Alt based keyboard shortcuts, e.g. Alt D F F for Data > Filter > AutoFilter still works.

If there was an alt-keyboard shortcut for paste removing duplicates, that should still work.

That's the point; the old shortcuts did not always work. Worse still, they did something totally different. For "power users", it was a horrible experience.