Would most people benefit from psychotherapy? At least in my country, undergoing psychotherapy is perceived negatively.
People in my country perceive people as either healthy (normal), or mad and in need of a psychologist. My perception is different. I think most people would benefit from psychological therapy. 

Does the evidence support the idea that most people would benefit from psychotherapy?
The same methods that psychotherapy utilizes to help people overcome psychological problems are used in coaching to help healthy and successful persons to become even more successful and feel even more better.

So, yes, everyone can benefit from psychotherapy, you just don't have to call it that, which might make it easier for most people to accept it.

If I were a psychotherapist, I would call my service "mental fitness" and advertise it in the same manner as gyms advertise their services as a lifestyle ("Be sexy and successful!") instead of a health product ("Fight obesity!").