It was most likely some specific detail of my previous old piss-poor Windows work computer environment but the ad-hoc, whole project + all_java_dependencies + entire_jdk full file scanning on every single file opened (no matter if it was the same file opened) by the Visual Studio Code for Java Language Service (remember, it's Windows, so under molasses slow file access/reading) made everything extremely painfully slow for me in Visual Studio Code.
Granted, JetBrains IntelliJ took 50s+ to open the project in such bad environment but it didn't constantly rescan the whole thing every time another file was opened.
Things seems to have been improving a lot (Visual Studio Code for Java Language Service Lightweight Mode and JetBrains Fleet Lightweight Mode comes to mind) since that, but it is still the reason why I use those JetBrains IDEs at all.