This is not true. The present value of cash today is higher then the present value of cash tomorrow. A dividend allows a shareholder to receive cash today while still owning the same percentage of the company. A share buyback allows a shareholder to give up future cash flow in exchange for cash today.
What you mean is the present value of 'x' units of cash today is higher than the present value of 'x' units of cash tomorrow.
If you look at pure IRR, dividends and share buybacks are
exactly the same. It is only taxes which make one form more efficient than the other.