Your protagonist's hardest sacrifice: a defense that works
What your protagonist gives up to earn their Strength is a defense that still works, which is why it's frightening and why it comes back as the last temptation.
Who your protagonist's ability is for after they change
The Truth doesn't give your protagonist a new ability; it changes the old one from protecting them to serving other people.
Your protagonist's big change shouldn't add an ability. It should change who the ability is for.
All story long, their ability protects them. At the end, it protects someone else.
Until then, the ability is stuck inside what StoryDNA calls The Weakness. That's a behavior that protects The Lie, a false belief your protagonist adopted to feel safe. It serves The Want, the goal they chase to stay safe, over The Need, the change that would make them whole.
Then your protagonist reaches The Truth: the corrected belief that replaces The Lie. Nothing new gets added. The same ability turns toward other people, and that's The Strength.
Tenacity stops proving a point and starts protecting someone. Perception stops manipulating and starts understanding.
Your protagonist can still get more skilled in the middle of your story. What The Truth changes is the direction the skill points.
In Erin Brockovich, Erin's bluntness costs her job after job. Then it becomes the force that holds a corporation to account.
A truth rarely gives anyone a new ability. It changes what the one they have is for.
Take the ability your protagonist uses to protect themselves early on, and write the scene where they use that same ability for someone else. Your reader should think, "Of course. That's what it was for."
Three ways a flaw keeps your protagonist's strength hidden
Your protagonist's Weakness keeps their Strength out of use in one of three ways, and the release has to undo that same way.