You need to highlight first and only then to press ctrl-I. So yes, typing is faster if you do it a lot.
If you're writing a new sentence in MSWord, you type "Emphasize words <Ctrl-I>like this<Ctrl-I>."
If you write a new sentence in Markdown, you type "Emphasize words *like this*."
The keys are neighbors even, at least in a US keyboard layout, so there is not a reason most US users would say it's "faster" to type * than Ctrl-I. (And if other layout users disagree, okay, but I don't think that was in the scope of the original point.)
The problem with Word-like editor styling is exactly that the boundaries are invisible, and the style is applied destructively to everything within highlighted range, instead of non-destructively by the range itself. What I mean is, if in the example above, I want to change the emphasis to only italicize "this", I can kill the first * and place it a word later. In Word-style editing, I'll have to highlight the whole "like " sequence and un-italicize it, hoping I didn't miss a space or a dot that invisibly retains the italics and then screw up editing for you down the line.
Is this very different from "<left> <Ctrl+Shift+left> <Ctrl+Shift+Left> <Ctrl+I>"?
What I also know is that when out company switched to visual editor only, people stopped using these. They stopped writing long texts - and those were those the most valuable.