For example, I find it much more productive to use Emacs for writing heavy tasks, where you'll spend a lot of time in the editor. Such as coding, writing notes, a book, an article, a paper, etc.
To me, these tasks suffer from having to switch back and forth between modes, and emacs just provides more features for them and can be customized endlessly to your specifics.
Vim on the other hand shines for quick edits, touch ups, or reading, viewing and analysing use cases.
Its best feature is performance. It starts fast, runs fast, can handle big files, consumes little memory and is small in size. This is ideal on a server, or as a default editor. I wouldn't want to have Emacs for these, it's too heavy.
For editing small parts of an existing file, the modal editing is also best. It makes navigation front and center, which is what you want, quickly find the part to edit, and quickly edit it, done.
I personally like it this way. I don't actually want Vim to grow to approach Emacs in customization. I also don't think anything can, the fundamental design of Emacs as a Lisp REPL with an editor loaded into it just can't be beat for that.