The idea that you are somehow enslaved by a predefined, concrete purpose that requires you to find power is toxic and must be killed. A person is capable of matching their means with their desired ends and finding meaning while avoiding the trap of needing power. You may arrive at power or influence, but I'd argue that should never be required.
A purpose can (and should) be defined by a process, and a motivation, and a living philosophy more so than a tangible number.
You can have power, and use it for good. But the toxic idea is that you must pursue power first, and that you must pursue power to fulfill some in-born, per-defined reason.
Warren Buffet did not set out to make billions of dollars of donations. He wanted to be a businessman, and ended up rich. Great, he's trying to do right by the billions he has, but could have probably had a bigger impact over the course of his lifetime by being directed at helping first and foremost.
You send a message that sets a chain of events in motion that saves millions. A common trope in fiction, with some basis in reality(e.g. the nuclear attack warnings during the Cold War, which a few soldiers in bunkers decided to ignore).
Power just means you get to call shots and take credit. It doesn't mean that you were the most valuable player.
I'm not sure that purpose is always so created. For me, it seems to arise from within. A deep, slow, emergent, understanding of purpose. I did not choose it, it came to me while I was busy with surviving. Perhaps I could choose another, perhaps I could re architect my personality. But would that ever be as authentic as the thing that first came into the light? Would it ever be as truly my own as some new construction?
We create ourselves to some extent, but also we are born. To deny that part of us which is born is a great shame.
A purpose can (and should) be defined by a process, and a motivation, and a living philosophy more so than a tangible number.
(edited to clarify)