For point #1--we've had Disney+ since launch, now this may just be my kids, but I'll try to encourage them to watch some of the older classics (Cinderella, Dumbo, Snow White, Jungle Book, Peter Pan, etc), and they don't. Maybe it's the way the animation style is, or it just "looks" old, but they just are not that interested. Little Mermaid is probably as far back as they'll go. They absolutely love the newer stuff though.
The thing is that I was born in 89 and you can bet I wasn't around when the classics came out and I still saw them.
But putting aside whether or not Disney should only take IPs from the 2000s and on for the new generations, the point is that the problem with Harmonious and Enchantment is not only the IPs, but the whole show in general. There is absolutely no story or writing for these shows. They are not telling a story, there is no connective tissue between the first clip to the last one. For a company that prides itself about caring first and foremost about the story they tell, it is puzzling that these marquee shows for the 50th anniversary have no reason to be. Using newer IPs shouldn't be anathema, but that's all Disney is using of late. Take Fantasmic. They updated
Disneyland's version with new IP's, but it works there because the show as a whole is telling a story. You understand why The Lion King is there or why Tangled is there or why Pirates of the Caribbeans is there. They are telling a story, they are tied together by something. Even as new IPs, they fit in the show's story. Not here. Plus they took the most underground songs and movies to do the 50th anniversary show. I like The Hunchback of Notre Dame but for the love of God I don't understand why 1/3 of Harmonious is about the Hunchback. For a 50th anniversary you need to honor the past, the rich history behind you, while aknowledging the generation that is coming. You need to bring both together. These shows don't even care to attempt that. Hell, they don't even attempt to tell a story and that's the biggest problem, regardless of what IP's they use. It's a mashup of Disney's IPs and not a very good one at that.
Disneyland shows how to make a proper anniversary show. Remember, Dreams Come True is the perfect 50th anniversary show. You have Walt's words, Walt's vid, they tell a story. They take you around Disneyland, because you hop in into the Railroad. You see a tribute to the attractions because you are "traveling" around Disneyland. You get a shout out to the Main Street Electrical Parade, you even get a freaking shout out to the classic Public Safety recordings on the rides for crying out loud (which is a nice touch because it is part of the experience). They honor the attractions that actually make you come back to the park.
Even for the 60th anniversary show, Disneyland Forever, which wasn't as well regarded as the one for the 50th, they take you to the orange groves where Disneyland stands today. You hear Walt's words and in the end you see Walt walking hand in hand with Mickey. That is a proper tribute. You honor the past and the park that you are celebrating. This is not a Walt Disney Company anniversary show, it's a WDW anniversary show. Enchantment and Harmonious are the signs of what's to come and that Disney might enter a new Dark Age. People are catching on and noticing what the new company philosophy is. With the new changes with Genie + and now seeing what kind of shows and attractions are being offered, many are rethinking their trips. You can see it in the comments of the official accounts on Youtube. The one for Genie + has so much hate there and the one for Harmonious is surprisingly full of disappointment too. Suprising because I didn't read a single positive comment for the show. That's not hyperbole. Go and read the comments. There is not a single positive comment
All in all, returning to the original critique... the shows are bad not because of the newer IPs (though I case can be made for Moana, Brave, The Hunchback and... Soul?), they are bad because they didn't bother with their cardinal rule: you gotta tell a story.