Why can’t I find a good IDE?

> if you want dark themes, you have to go through every language you use and set all the colors for each text type (comments, selected, functions, etc). This requires probably 300 clicks for each language. (...) what am I missing

I'd change colors for one language, check where the settings are saved (Linux: probably some dot something folder in your home folder) change ONE color for every other language, see how those are stored and write a script (I'd probably use Perl or Python, feel free to use anything else if it's faster for you) to "fill in the blanks" for the rest. I think I can do this very fast, matter of only a few minutes, and I'd save the scripts for any other occasion (or maybe saving a resulting color settings section is enough).

I don't use Eclipse, but I guess it's doable as I describe.

Alternatively, if I wouldn't be able to use script for some reason (binary stored settings?) I'd simply change the colors for the language I want to use at that moment. I'd postpone changing anything else until I need that something else. There's big chance that it would result in one language configured every other day, and that some languages that I think I'd need never get configured as I haven't had to really use them from Eclipse or whatever.

TextMate IS the all-in-one champ.

The question should be which language-specific IDEs are so good they're worth deviating for.