"Necessary" is a strong word. It's acceptable IMO, and my kids like it. If you want some more reasons:
- I strongly feel my children have agency, within reason. They like it, more than Disney+, and it's not a strong detractor.
- Frankly, most of the YT stuff they watch is, really, more appropriate. Bite-sized sciency or crafty things, with a silly song. Disney+ stuff I could find myself was genuinely either a bit boring, or a bit naff, or for older children. [EDIT] Timeless classics like Lion King are often too scary for them, and there's plenty of inappropriate stuff there too, just due to the passage of time. Let's just say, Snow White and the Seven Dwarves hasn't aged well.
- There is a much wider selection. My younger daughter is fascinated by aeroplanes. She watches video after video of planes taking off and landing, helicopters hovering and so on. Where do I find it on Disney+?
- Sometimes I see things I don't like on YT, it's a one-click ban for the creator. I have never seen anything wildly inappropriate. It's maybe an issue if your kids are watching it for hours on end, not so much if it's 20 mins after dinner, and I'm in the room.
I was talking to my mum about this, who remembers the same laments about letting children listen to the radio (mindless entertainment, no parental control), and her mum remembers the same thing about children being allowed to read their own colorful children's books, as opposed to adults reading a boring small-print book. When my younger cousins were growing up, there was family lament that they meet up with friends and play video games - yet they didn't grow up to be antisocial psychos. IMO we tend to over-demonise the new.