One thing I'm missing in all these languages is 100% auto-completion like the one you have in Java or C#. I have yet to experience a single instance of Intellij not being able to auto-complete something or not do it completely.

I know Nim and Rust have good VS Code plugins that do that to some extent but it is not something I can rely upon.

Maybe I'm just spoiled.

There is an official Nim plugin from JetBrains now. It won't be as polished as Java support for obvious reasons, but at least you can stick with your preferred environment.

In which editor? This would really help me. IdE support and no pandas/numpy are the main things holding me back from full nim adoption

There is NimData [1] and ggplotnim [2] and Arraymancer [3]. Also, neovim works well with the alaviss plugin [4], though it's not quite a full IDE. Most Nim coders use VS.

[1] https://github.com/bluenote10/NimData

[2] https://github.com/Vindaar/ggplotnim

[3] https://github.com/mratsim/Arraymancer

[4] https://github.com/alaviss/nim.nvim