Apart from the question of complexity, the language gives insight into the thinking of the people speaking it. Once you start to learn a language and get beyond a certain basic level, all sorts of wonderful things open up - the language as a window into their thinking, how they formulate certain concepts, how they view their surroundings and their interaction with others.
That has been interesting from working with Australian Aboriginal people - English is often their 3rd of 4th ‘foreign’ language, and many concepts they are exposed to by the modern Australian society lacks words in their own language, so they create new descriptive words for that and then translate them literally into English. Or often they absorb the English term into their language. Anyway, fascinating topic … sorry, I’m rambling.
Interesting, thanks! Yes, that's another controversy that I am working on. And I think that part of the problem is that linguists (like biologists) don't dare go there, and think of people as a dog breeder would think of doggies: the same species, with varieties. If they only did that, they may realize that there are some differences in thought, and that not all of them are simple "cultural".
Borrowing is also a fascinating topic, and as you pointed out, there are different mechanisms by which that is done. The problem is that then, a BIG leap has been made, and the consensus is that borrowing leads to a new language (say, from Latin to Romance languages, or from Anglo-Saxon to English). The more I read, the more I'm convinced that cannot be the case. Not even to explain why there seem to be so much French in English, for example. More later!