Well sure, if you compare vim to some kind of strawman notepad user it's gonna look pretty good. But if you compare it with someone who's put a fraction as much effort into learning a modern editor, the benefits seem a lot more dubious.

e.g. in Sublime:

>if I want to duplicate a line

Ctrl-Shift-D

>If I want to change the contents of a quoted string

Ctrl-Shift-M selects inside parens. It doesn't do quotes by default, but there might be a way to enable that.

EDIT: I looked this up afterwards, and discovered Ctrl-Shift-Space selects a quoted (or parened) block, although it includes the quotes.

>If I want to change each line from the current line to the next blank line to a continuous quoted string

Okay, this seems a bit contrived, and I'm not convinced the average vim user would bother with this rather than just doing something like I"<Esc>}kA" or whatever.

Unless you're bulk editing, in which case I think Sublime's regex find and replace would be similarly effective, and probably easier to get right than typing the whole command in one.

I will note however that selecting text and pressing a paren key wraps it in parens, and as above it might be possible to make that work for quotes.