A balance of Fi and Te are best for those with aux/tert Fi and Te. They have opposite uses though due to what we lean towards for cetain use cases. Eric B has touched on this concept though i dont know any technical theories or names. Just what i see with my own eyes.
Completely agree with "hapiness is being capable of handling your problems in a way that aligns with you as a whole". This is where we need to know how to best handle things for ourselves. For example an ENFJ will need to handle a situation different then an ISTP because function wise we have different strengths, weaknesses that aside from experience is based on our different use and how they steer the outlook on our life. For me Fi is a background process. During down times i equate it to walking through a swamp just looking at my emotions and the values i have. Its like a view into myself. Where as a more dom Fi has it more at the forefront and its a deciding and controlling factor. Mine only controls when it explodes and at that point its forceful and out of my control. I live my life to where that doesnt happen very much so for the most part Fi is just part of who i am, but doesnt define who i am externally.