As for Python performance, on the contrary, I think there was a large portion of the Python community that did care during my years with it. I think 3.x adoption was hurt a lot by being slower than 2.7.x. I think a lot of the community jumped ship to Golang or similar, for both performance and complexity reasons.
I would absolutely love for C++ to tackle C UB or make incompatible insecure C. Instead, we get stuff like Ranges, time and again. I'm struggling to understand what complexities you are finding it covers that are worth supporting forever, committing gray matter, committing productivity loss, committing debug travesties, &c. Say I'm a musician that can hold complete compositions in my head; why should I commit this feature and its baggage to memory?