I agree, the "5dd" example is super contrived, though not as much as you think. In vim, you can have the line numbers on the left show you numbers relative to your current line, so you never really have to count, you can just look at the number on the line you want to go to.
But outside of that, the problem with standard editors is that none of your keyboard shortcuts compose together. You have special shortcuts for deleting lines vs deleting individual words. No shortcut for copying objects to your clipboard. No shortcuts for "get me what's within these parens". You can't move between panes with consistent keybindings, because most editors represent code panes vs directory panes differently.
Vim lets you think of editing and navigating your code in terms of verbs and objects, and treats everything consistently. Take the "w" object, that's "word". Now I can move around by word by mashing "w", I can delete with "dw", change with "cw", yank to clipboard with "yw". The "." command lets me repeat, so I can do things like "dw..." and delete more easily. Some plugins add more objects, like being able to refer to surrounded text (e.g., in parentheses.) They compose with all the verbs you already know, so now I can delete inside parens, surround with parens, replace text within parens, copy in parens, etc.
Vim compared to standard text editors is like functional vs imperative programming. It works best for code, because editing code is not like writing prose. You're manipulating a syntax tree.