Are you sure the problem is existential?

Solving the correct problem?

What about rich heiresses with everything in the world available to buy, who still feel unhappy? Perhaps they can't get themselves into satisfying romantic relationships. One way or another, they don't know how to use their money to create happiness - they lack the expertise in hedonic psychology and/or self-awareness and/or simple competence.

So they're constantly unhappy - and they blame it on existential angst, because they've already solved the only problem they know how to solve. They already have enough money and they've already bought all the toys. Clearly, if there's still a problem, it's because life is meaningless.

If someone who weighs 560 pounds suffers from "existential angst", allegedly because the universe is a mere dance of particles, then stomach reduction surgery might drastically change their views of the metaphysics of morality.