"the IDE had to be discoverable right away (which it was) and self-contained to offer you a complete development experience"

This right here was the key to super flow state. Lightning fast help (F1), very terse and straightforward manuals. I have tried to replicate this with things like Dash (https://kapeli.com/dash), to some degree of success.

The closest thing I had to this in windows was probably Visual Studio 6 before the MSDN added everything that wasn't C/C++ to the help docs. After that, the docs got much harder to use due to their not being single purpose anymore. The IDE was a little more complex, but you at least felt like you got something for it. After that, too many languages, too many features, overall not great experience.

The keybindings were so simple and fast, Borland IDE on DOS was a very nice tool. Yes, easier than vim and emacs. The reason is because of mouse in TUI so things like complex selection/blocks/text manipulation are not keybindings in the same way so the key combos are more "programming meta"(build, debug, etc) rather than "text meta".

EDIT: also, I feel like this needs to be mentioned: compilers were not free (as in beer) at that time!

In order to develop on my own machine as a teen, I had to sneakily copy the floppy disks the teacher used to install this on the school computers so I could have more than 1h using it at home! COPY THAT FLOPPY