Yeah. w3schools sucks imo. It's full of outdated or incomplete information. MDN not only gives more up to date info, it's also more comprehensive. Sometimes it also gives some good guidelines to wether use something or use an alternative etc.
I totally agree with w3schools being bad. However, when teaching web dev to beginner students, they usually find the MDN hard to understand and turn to w3schools.
The MDN requires either quite a lot of experience reading documentation, or being shown how to navigate it.
W3s is where is starts for me. Then move to MDN for more specific and in depth things. W3s just gives the best examples and has that lovely playground for every documentation step.
Just want to drop devdocs.io here for anyone who might benefit. It's an aggregation of many different popular documentation works from different projects. All in one place. One tab. Imagine one tab of documentation.