Of what use is power if you don’t have it long enough to do anything? The most powerful leader of all time should not only be able to accumulate power, but they should have had it long enough to wield it.
Ashoka held his kingdom for almost half a century, far longer than many other historical figures that managed to accumulate vast amounts of power. After the conquest in his ascent to power, he renounced violence and war. Considering many of the most powerful rulers in history acquired their land and power through war and violence, Ashoka's decision to follow the tenets of Buddhism and abstain from violent practices is impressive.  His power was maintained through his values, and not by his armies. The same cannot be said for many of the great rulers through human history. He communicated with people through his virtues, respecting the personal beliefs of many of his subjects. In many ways, he fostered an open society more than a millennium before the Enlightenment.
Emperor Ashoka may have had a grip on power for his lifetime, but he was unable to sustain a multi-generational kingdom. His successor inherited a declining empire and lost control of some of the territories that Ashoka once held. Other empires, such as Rome, were able to maintain centuries of power through economic, military, and geographical dominance. If Ashoka had maintained power over India through force, he would have perhaps passed on a more stable empire to his successors. Instead, Ashoka's power died with him.
It takes far more effort to retain power than accumulate power. Those that can accumulate and then maintain power have far more real power than those that can accumulate it quickly but cannot hold it.
[P1] The real measure of power is not how much you accumulate, but how long you retain it. [P2] Ashoka was able to retain his empire for half a century. [P3] He maintained his power without violence and war, but, rather, through values.
Rejecting the premises
[Rejecting P1] The measure of power is better done by land occupied, the size of the military, and wealth. [Rejecting P2] Ashoka may have maintained power for his lifetime, but his kingdom declined soon after. [Rejecting P3] Maintaining power through force guarantees the longevity of the empire as a whole.