(There are some examples of molecules families. You have many variants of it encoded in the DNA, and each is optimized for a different task. IIRC the idea is that some molecule is used for two similar thing, then after a lot of generations by a random chance you get two copies of the code in the DNA, then after a lot of generations each copy is used for one task, then after a lot of generations each copy evolves to be optimized for it's task. See the variants in https://en.wikipedia.org/wiki/Hemoglobin#Types_in_humans and also the distant variant https://en.wikipedia.org/wiki/Myoglobin )
Why produce insuulin if you can’t use it. The mere presence of that sequence may have consequences for other development. Some sequences may be if, then, else statements, there is so much we don’t understand.
We are playing russian roulette, except the number of bullets changes every round.
But we’ve done this before, “humans can’t possibly alter the global environment”. Even climate scientists were saying that until about 20 years ago.
Some parts have a very straightforward meaning. For example the DNA code for insulin is well known and understood, you can copy it to bacteria to make them produce a 100% accurate version of human insulin. https://en.wikipedia.org/wiki/Insulin
> The human insulin protein is composed of 51 amino acids, and has a molecular mass of 5808 Da. It is a dimer of an A-chain and a B-chain, which are linked together by disulfide bonds. Insulin's structure varies slightly between species of animals. Insulin from animal sources differs somewhat in effectiveness (in carbohydrate metabolism effects) from human insulin because of these variations. Porcine insulin is especially close to the human version, and was widely used to treat type 1 diabetics before human insulin could be produced in large quantities by recombinant DNA technologies.
Many enzymes have also a similar straightforward DNA->protein->function story.
(The regulation method to decide what enzymes to produce and how much of them is more complicated, but some are well known.)
If you want to identify the genes for more general traits like height or intelligence, then you will get something like what you said, that is a very complicated interaction on many genes that we don't understand.