To me, how you talk about 'avoiding unhappiness' is a bit unclear. I agree it is healthy to be unhappy sometimes, and it is unwise to seek out an existence where one is
never unhappy ever. That never-ever-unhappiness is a state I agree we should not try to avoid.
However, it also sounds like you're saying that we should never try and avoid each
individual instance of unhappiness from
every situation. If so, this is dangerous advice. Sometimes, our environments provide us with enough unhappy stimuli that if we experience unhappiness for each stimulus, we are experiencing unhappiness more quickly than is healthy. Unhealthy rates of unhappiness can prevent us from feeling and expressing other parts of ourselves, and can contribute to unhappiness becoming a part of our identity we struggle to deviate from, leading to even more unhealthy unhappiness in a trapping cycle.
If we are experiencing unhealthy levels of unhappiness, if it is possible and reasonable to do so, we should change our environment or our experience of feelings to decrease our unhappiness to a healthy rate. For example, if someone is doomscrolling constantly, taking in constant negative stimulus and experiencing constant unhappiness, they should not continue in this complex experience. Instead, they should solve a flaw in their environment, they should stop doomscrolling, instead of taking on each individual feeling of unhappiness.
While I agree with some of your points, and also did not get much help from attempting therapy, I think your post is also missing a bigger-scale point. Happiness / solving problems and experiencing situations aren't alternatives that we choose between, they are complements we can do together and which make the other better. A baseball game is something to be experienced, not solved, but if you figure out why your car keeps breaking down on the highway and fix that before you drive out to the stadium, you're probably going to have a richer experience.
Finding the root of our problems can also help us better understand them, making our experience of unhappiness more complete and richer. For example, if one newly understands that they are insecure about their body because they were bullied for it in the past, they can add compassion for their past self into these experiences of insecurity. Not necessarily preventing these experiences or removing them altogether, but adding a valuable dimension of complexity to them.
This role, where patients are better able to have richer experiences, as opposed to shutting out all unhappiness, is what competent therapy should strive for.
I've talked a bit about solving problems improving our experiences, but I'll also note some specific benefits of happiness, besides the obvious note that happy experiences are often desirable experiences. Happiness increases our confidence, our acceptance of risk, and our initiative to take actions of our own accord versus just reactivity and passivity. For example, a study in a reputable academic journal found that happier participants, versus sadder participants, trusted their own thoughts more and cared more about an argument's quality before adopting it, being less susceptible to manipulation from weak arguments. (
Source. I also provide a graph from the full article below.)