The problem is that you used vague sophist dialogue that could turn either way. You could say that T G A C are the designed parts, or any kind of bullshit honestly.

It's bad communication. You need to follow up the vague analogies with real examples to make a message stick. If you don't, people have no idea what you are saying.

I assure you that both my leg and desk lamps are perfectly real. There is a common kind of desk lamp that is even fairly mechanically similar to a human leg, with a knee , tension springs, and a ball-and-socket joint to permit free repositioning in multiple degrees of freedom, and about the same size. But the different design processes involved have resulted in very different designs, and a major reason for that is precisely the use of standardized parts in the desk lamp, but not in my leg, which results precisely from the kind of specialization we have been talking about. I don't see how much less vague I could have been. Are you being sarcastic?

A human leg isn't designed to be repaired from the outside, it doesn't need replacement parts, it doesn't need external maintenance. It's designed around the maintenance and repair procedures of the human body which are able to fix it in situ and produce new parts on the fly. That allows it to have more freedom of design than a mechanical part that needs to be made from standardized parts in order to be serviced and manufactured.

The limitation is not cognitive, it's a matter of efficiency. We could, if we wanted to, make a lamp with all custom parts with the maximum efficiency possible in the design, but those efficiency gains would be at the cost of extremely difficult manufacturing. It's a tradeoff that the human body can make because it needs to produce only one (or two) legs, while us humans mass manufacture the stuff we make.

It sounds like you're more in favor of unique parts made to fit specific applications, wheras I prefer the more modern style of mostly generic parts with mostly only the case design and the code being unique

It's more nuanced than that. Unique parts made to fit specific applications can clearly perform better, but that doesn't mean I'm in favor of them in all contexts. Rather, I'm observing that the reason we don't use them for things like desk lamps, instead using mostly generic parts, is because of our cognitive limitations, which we cope with through specialization and generic parts with loosely-coupled, independent designs. This is a form of "dividing and specializing design", which is what alganet was saying people shouldn't do.

I am not in favor of ignoring those cognitive limitations. That wouldn't make the limitations go away; it would only keep us from taking measures to cope with them, such as dividing and specializing design into modular generic parts.