Well, I had carefully curated some quotes to respond to, but they were lost in an ooopsie on my part and I am not going to wade through 107 pages of content to find them again. Let's see if I can bulletpoint some of the salient thoughts.
First off, I am a 1e/2e grognard that came back a year ago after a zillion years away. I've said this elsewhere, but it bears saying again, as it's relevant.
1) In my view, 5e catered to a whole videogamey generation that couldn't handle their characters being squished dead. It does cater to munchkins. Just look at all the "this build is overpowered, here's how you can do it too" Youtube videos. None of them are about creating characters, they're about being unbeatable. This isn't new .... the only difference between the stuff encoded in the game and when I was a kid in high school is that the kids in high school had third-level paladins with Holy Avengers and Girdles of Giant Strength while wearing +5 plate. You're never going to avoid that mentality .... it's kinda human. But encoding it into the rules encourages the problem.
2) looking through a lens of coming back to D&D after a gazillion years away, it's obvious that this has been the direction the game has taken. Every class has magic, humans are boring. There's eighty-seven playable races, sixty-zillion subclasses. It's gone too far.
3) I saw one post that said it should take two sessions to get to third level. WTF? I've had a game running for almost a year now, 35 sessions. 1e/2e homebrew. Levels are 4,4, 3/3 3/3 and an npc 4. We're getting to the good stuff.
4) The joy of the old school game is that your third-level rogue might very well die an hour into exploring wherever. Oh well. We always had backup characters, right? I remember introducing a dwarven fighter into a game ... I spent days curating the dude's background. Half an hour into the session, he was offed by a critical hit from a Piercer. Oh well. Next up. The current system makes it difficult to kill a PC.
5) The whole CR thing is bunkum. It's a kludge because the system is now so broken that it's difficult to figure out how to challenge a PC party, especially with the extra actions, reactions, bonus actions and other stuff that's been added to make action economy more valuable.
6) Not everything 5e did is trash. That's the thing about systems. I like how they have the skill system.
7) I am now a firm believer in point buy for stats. This seems to have been normalized. That's good.
The dude who wrote "the monsters know what they're doing" isn't wrong. There's a reason a whole bunch of us still tinker with homebrew alterations of the old systems. The old systems weren't perfect either, but they allow a grittier background.