I think two out of those believes stem from survivorship bias. You think of old music and consumer products as superior because the only ones that "survived" are the good ones. No one remembers bad music from 50 years ago, and for every old thermos flask/blender/knife that you see around there are dozens that broke years ago.
There was song from the 60s (supposedly the best music everyone tells me) called "7 little girls". The chorus went "7 little girls sitting the back seat kissing and hugging with Fred"
Thankfully a mostly forgotten song now, but a clear example of how bloody awful pop music is not a new phenomenon.
I say yes for the music one, maybe not for the first. There are literally different materials being used and increasingly optimised-for-profit-to-effort-ratio processes. Many things are just straight up made more cheaply because we have the technology to do that.
Although for the music one, a relevant lyric comes to mind:
Hip hop is pretty mainstream now but it started as counter culture. And I don't think a sample in a song makes it similar to the sampled song. A lot of tracks that rely on samples completely create something new. Look at J Dilla who relied almost entirely on samples. His music isn't a collection of old songs, it's entirely new songs. I guess this thread is for boomer takes.
My theory on the first one is that it's usually hard to make things cheap and consistent, so it often starts off as bad, then good but expensive, and then trends towards and past "good enough"
Modern music is fire when you know where to look but I've always felt like pop music has been taking a very slow weird turn. It seems like 1970s and earlier it was mostly good, and mostly good after, but at this point I'm just confused