Building off of VSCode was probably Cursors silver bullet and the best decision they could have ever made.
It made migrating for everyone using VSCode (probably the single most popular editor) or another vscode forked editor (but at the time it was basically all VSCode) as simple as install and import settings.
I do not think Cursor would have done nearly as well as it has if it didn't. So even though it can be subpar in some areas due to VSCodes baggage, its probably staying that way for a while.
I dont disagree with anything you said. If I was in their shoes, I would have done exactly the same thing.
Maybe my complaint is that I wish vscode had more features like intellij, or that intellij was the open source baseline a lot of other things could be built on.
Intellij is not without its cruft and problems, dont get me wrong. But its git integration, search, navigation, database tools - I could go on - all of these features are just so much nicer than what vscode offers.