I think "necessary" is a strong word. I would say that it is "helpful" for me, since I can fine tune the behavior. For example, DND was all or nothing (except for favorite contacts for Apple apps like Phone, Messages, etc.), but now I can allow certain third-party apps to notify me as usual while silencing all other apps. I had wanted this for a long time before. Say, your family only uses Telegram to text one another. You can turn on the new DND/Focus and silence everything except for Telegram. You could not do that before.
It's not all about the home screens. I don't care about that part at all, as I have only one home screen and the app library. But I can imagine how it can be useful for many people. It is not about distraction either, but convenience. Imagine you have 8 home screens and the app library. Instead of having to swipe 4, 5, 6, times to get to a screen or the app library, you can organize the home screens and eliminate the irrelevant ones in different situations so that you need to only swipe 1 or 2 times to get to your apps or the app library.