It's the fundamental goal of the rules that they have trouble grasping. Then instead of coming to the conclusion that maybe they're not reading them correctly they declare the game broken. Hubris. Unfortunately I've found that for the most stubborn no matter how many videos like that you show them they will refuse to budge. And for those new to the game they don't need the video as they tend to just get it.
When people say that some kind of rule is "broken" it means "it doesn't match my expectations". Sometimes the expectations are just stupid and there are no grounds for having such expectations.
Sometimes, well, they are pretty reasonable. Stealth is one of them -- if I can build a sneaky character, I generally expect to have some more reproducible and reliable rules that govern sneaking around. Well, to be honest, there are such rules but they are spread so thinly all over the PHB (and maybe the DMG, I don't really remember) and figuring them out requires some effort. But I've very rarely seen people who call 5e stealth rules "broken", in my experience, people more often just find them confusing.
Another example would be yo-yo healing pattern. It's pretty reasonable within the design of the game (healing is purposefully weak, so there can be no healbots), but at the same time, it's kind of stupid. It doesn't really make sense "on screen", so I can certainly see some people thinking that it's broken.
As of new players better getting the rules -- it also comes down to expectations and is apparent pretty much everywhere. There's a point where people can't just grasp that something may work differently than what they're accustomed to. New programmers "get" functional programming faster than those who are accustomed to OOP, but slower than those who know enough to know when to leave their expectations at the door; when I was learning my second language I had a really hard time, but now I know that there's no reason to expect Finnish work the same way as any of them I already speak; new players get 5e faster than 3.5e players who can't figure out why the hell standing up doesn't provoke AoOs; etc; etc; etc.
It's even more apparent outside of D&D, but I talk about other systems on this board way too much, so I'll shut up.