Maybe the approach by only hierarchical considerations of structures (from the system down to the elements which constitute it) stops to be performant for complex systems and must be replace by considerations using emergence concepts.

For instance, the multiple interactions between the diverses components and the different levels lead to new properties of system level which cannot be reduced to those of each component by analytical way. Components of aircraft, automobile or trees are themselves composed of deeper systems, themselves also complex, like cristalline structures, molecules, genes, and also environmental outputs and inputs, and these elements are themselves composed of atoms, radiations fields, etc.

The main difficulty is, without falling in a superficial hollistic approach, to identify at each level of system and components which are those pertinent to consider in regard of the aim of the problem, the actual use (that we can call "intentionality" in study of system), and to define the frontiers which define the domain of validity of modelling.

By the way, it is the aeternal problem about the relation between reductionism and systemic approaches.

But, i suppose you have already thought about it.

From my perspective, although we may utimately discover that many mental health conditions have a biological explanation, at present explanations at this level of anaylysis offer some assistance, but other issues (e.g., thoughts, feelings) also need to be considered. For example, neurochemical theories of depression have proven useful in the development of a large range of medications that help clients address issues with depression; however, cognitive behaviour therapy has been found to be a very effective treatment for depression as well. The same logic may apply to a wide range of other conditions as well.