The link seems to be dead but here's my thought anyway.
People in this thread mentioned brilliant factors among those IDE/editors, but the 2 cents I want to add is their difference is related to the way they work, or how people work on them.
VSCode: LSP reflects the mentality of VSCode - it's extensible, it's working but it usually doesn't offer first-class experiences. It usually aims to serve the intersection or the common part of languages first, then the specific language.
The idea is very akin to Emacs, in which the community tries to find the abstraction of functionality, and then people can work on different implementations at the same time - there's Helm for completion, and Flycheck for checking in the first place, then there's a whole bunch of implementations. The good is it solves the m*n problem, but the bad is the experience is not good as tailored for specific languages. Actually, one specific struggle in the Emacs community right now is choosing between LSP and language-specific plugins.
Intellij: It is on the other side of the spectrum. It's polished, feels pragmatic for major languages they're targeting. Unlike LSP and VSCode, It was aimed to be the best Java IDE, and it did it. Now you can see the inheritance panel for a lot of languages that don't even really care about inheritance.
So IMO it's like Conway's law. The key difference between VSCode and Intellij is because of the way they work - VSCode was built on community, and Microsoft is more like a facilitator. While IntelliJ is driven by a single company, and the plugins and communities are supplement features.
People in this thread mentioned brilliant factors among those IDE/editors, but the 2 cents I want to add is their difference is related to the way they work, or how people work on them.
VSCode: LSP reflects the mentality of VSCode - it's extensible, it's working but it usually doesn't offer first-class experiences. It usually aims to serve the intersection or the common part of languages first, then the specific language.
The idea is very akin to Emacs, in which the community tries to find the abstraction of functionality, and then people can work on different implementations at the same time - there's Helm for completion, and Flycheck for checking in the first place, then there's a whole bunch of implementations. The good is it solves the m*n problem, but the bad is the experience is not good as tailored for specific languages. Actually, one specific struggle in the Emacs community right now is choosing between LSP and language-specific plugins.
Intellij: It is on the other side of the spectrum. It's polished, feels pragmatic for major languages they're targeting. Unlike LSP and VSCode, It was aimed to be the best Java IDE, and it did it. Now you can see the inheritance panel for a lot of languages that don't even really care about inheritance.
So IMO it's like Conway's law. The key difference between VSCode and Intellij is because of the way they work - VSCode was built on community, and Microsoft is more like a facilitator. While IntelliJ is driven by a single company, and the plugins and communities are supplement features.