"People who have power look for fights. People who don't have power lose everything." - - - Masashi Kishimoto
Who were the most powerful people in LOST?
Widmore was a powerful businessman who could do just about anything, including "faking" the 815 crash site with corpses. He was ruthless. He showed no mercy. He did everything he could get back control of the island, including sending mercenaries to kill everyone.
Ben was a powerful leader of the Others. He manipulated his followers by a combination of fear and mental brain washing. He also was ruthless and showed little mercy to his enemies. He helped wipe out Dharma compound by betraying his co-workers with nerve gas. That was his first coup; his second was exiling Widmore from the island.
Jacob was the island guardian. He had immense power of an immortal being. He could grant eternal life as he did to Alpert, but he could not bring back the dead to life. He could bring people to his island. He manipulated his followers through surrogates, adding a level hidden control over the people who believed in him. His followers would worship him but never see or hear him.
Eloise seemed to know everything about everyone. She knew the power of the island. She knew how to find the island. She knew how to manipulate people to get to the island. And she was the only person fully aware of what the sideways world was, and that awakening her son who make him leave her. If knowledge was power in the series (as I believe), then Eloise was a very powerful character who used it to her advantage.
But at the same time, Widmore lost his island conquest goal when he was killed by Ben.
Likewise, Ben lost his control and leadership of the Others when he killed Jacob.
And Jacob lost his followers when word spread that he had been killed by Ben and Flocke.
Widmore lost everything material in his life that he acquired under the most brutal means, but somehow he was rewarded with a blissful life in the sideways world.
Ben lost everything in his life, including his family, friends and followers, but he was somehow rewarded with a second chance in the sideways world where he did not have to move on. He was granted a similar reward as Eloise, the knowledge of the sideways world realm, and an opportunity to keep the fantasy world alive in his own mind.
Jacob had lost his family while on the island. He was trapped there as the light source guardian. He spent thousands of years trying to find a way to leave, but the smoke monster kept him imprisoned on the island. When ghost Jacob told the final candidates that when the fire (his light) would go out, he would be no more - - - it would seem that Jacob received no reward for his island service. He lost everything and everyone close to him.