Gender of nouns
Everyone agrees that the assignment of gender to nouns and subsequent case inflections are challenging for learners and natural for native speakers. Child acquisition studies have revealed that "adult-like" ability occurs around six. So, even native speakers go through a learning process. If that bothers you, do not read: Der Dativ ist dem Genitiv sein Tod Von Sebastian Sick.
I beg to disagree on this one. German is relatively simple. When my parents were young everybody who ever attended University in Brazil went through Latin, which they had to learn at a very high level. Everybody had to translate Ovid for the admission exams. That is way more difficult then modern German. And they were no geniuses. They simply studied hard, learning loads of things by heart and applying a lot of little rules, which they learned by heart as well. And no, they did not watch TV or had cell-phone apps nor anything of that sort.
The thing is, we feel challenged because we never had to learn that way, it's totally out-of-fashion in our times. Too bad.
Im not sure what you disagree with. The learning of any second language is a challenge. There is no real logic behind the assignment of gender. If you are saying studying and practice can help, I agree, but it still remains a challenge.
I think we dont' agree on how difficult it is to learn the gender of nouns. That is something you simply look up in any dictionary and I don't see that as a challenge, to be honest. When I started learning German, I used paper dictionaries. Now we have the ease of phone-apps. I had lived in Germany for many years, finished my studies there and don't remember native speakers challenged by the gender of nouns. Or maybe once, in a Mexican restaurant, when we argued over the gender of guacamole and tacos - which aren't German words (or German things).
And by the way I've read "Der Dativ ist dem Genitiv sein Tod". It's a good help for modern style German writing.
Then you should be familiar with the fact the assignment of gender can even challenge the native speaker.
I'm sorry to tell you, I read that book maybe 10 years ago, so I cannot recall it quite well. Whenever I go to Germany again, I'll sure bring up this subject of the assignment of gender to nouns with friends. And I must add: I love dictionaries, they are a staple of my day, along with coffee! Ich liebe Wörterbücher über alles!