Comment by OgsyedIE

Not necessarily. Diathesis is a broader term that includes congenital aspects, maternal stressors and various toxin exposures, among other things.

For example, restricting the range of discourse to the purely congenital excludes things like fetal alcohol syndrome, the ages of both parent's gametes and pre-natal exposure to endocrine disruptors. However, in everyday usage, the diathesis refers primarily to those of the symptoms in the physiology, psychology and behavior of the subject that aren't attributable to life experiences (good and bad) rather than the microbiology specifics that act as carriers for any specific cause.

What's important above all else for the psychiatric practice is effective decomposition of any disease into parts that are amenable to study and treatment, rather than comparison to the hypothetical of what kind of "peak" may be achievable for a specific genotype if everything else went well.

This may be useful:

https://en.wikipedia.org/wiki/Diathesis-stress_model