"Purposeful" does not help if we are mostly clueless.

So I don't see your point. It is really tuning for surviving within the constrains.

Let x be the set of all physical behaviors in nature. At any point in time, we (human beings) are aware of a subset of x, let us call it y.

When a human entity design a system, they can only use the behaviors in y. But an evolved system could potentially use all of x. This means that we will never be able to know everything required to safely modify an evolved system.

Also, evolved systems are hard to reverse engineer.

https://www.damninteresting.com/on-the-origin-of-circuits/

If something simple like an electronic circuit with comparatively short evolution can end up with mysterious, un-intutive and complex inter-dependent behavior, imagine how non-understandable an immune system that evolved over millions of years can be..

So I still think we are mostly clueless, and it is nearly impossible to safely engineer changes into something that was not engineered in the first place...

Electricity is a convenient example, because it's indisputable that we have leveraged it to do real work based on real understanding. I suspect any and every area of knowledge is subject to a kind complexity crash where the combinations of variables outstrip our ability to track them. But treating that like it negates the knowledge we do have is almost literally what it means to miss the forest for the trees.