> I cannot instantly create a new file

Agreed, but if you use IdeaVim you can:

  :e src/my_new_file.txt

> The startup times are just abysmal

For quick edits I just use Vim, but disabling unused plugins speeds up startup quite a bit.

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> Switching projects has abysmal performance

I reported that bug: https://youtrack.jetbrains.com/issue/JUNIE-2563/Minor-UX-Slo...