> Why is it so hard to see code from 5 minutes ago while in the middle of a change?
In vim you can do:
:earlier 5m
to see the code you had 5 minutes ago.
> (1) If you go to a prior state and then make a new change, you can no longer redo and all those changes are lost.
Vim makes a tree, so that doesn't happen with it. When you undo and make a new change, you're just making a new branch. u/Ctrl-r goes from leaf to trunk, but with g-/g+ or :earlier/:later you can walk the whole tree.
Emacs similarly doesn't lose changes in this scenario, but instead of making a tree, it has a ring and undo is an action that can be undone.
> (2) You can not see a side-by-side comparison of the previous version and the latest version.
It's probably not complicated to make a macro or function where you go to a previous version, copy the buffer, paste it in a new one on a new window, return the original buffer to the state you were in, and diff the windows for that side-by-side comparison.
A command like so suffices:
:earlier 5m | %y | later 5m | diffthis | vnew | put | 1d | diffthis
> (3) There is no visual indicator of where you are are in your undo/redo history.
Not by default, no. :undolist provides some info, though, and the vimscript undotree() function probably provides all the state of the undotree. There might be plugins that somehow present this info in the interface.
> (5) I have found many actions in code editors that do not get added to the undo stack (e.g., changing a debugger option), which caused me problems in the midst of an annoying bug.
In vim, only stuff that changes the buffer is added to the undo tree. Navigation or changes of the state of the editor (e.g. editor options or vimscript variables) aren't added. Are there really editors where adding actions that aren't changes make sense?
> (6) There is no indication of what steps were "big" or how long ago they happened.
That's also true in vim it seems, at least how "big" they where. Each step does have a timestamp, though.
> (6) It is tedious to backtrack one small step at a time.
You can backtrack by however many steps you want. :earlier also supports specifying by seconds, minutes, hours, days, or file writes.
Most cool of all is that vim can persist the undo history. I don't know how common that is among editors, but in vim you can go to a file you haven't opened in years and undo it all the way to its beginning.