It's as with any genre though, isn't it? A character type becomes a staple, and then then a stereotype of the genre. But it is a shame, because as a reader, you can look at that book, with that similar cookie-cutter protagonist, roll your eyes and wish for something a bit more original. And that can be such a shame, as there's actually a great plot going on, but sadly it's not being pursued by an original MC.
I guess you're right- it's a lot about setting up a character that'll make sales work over a very long story-arc of multiple books- and tried-and-tested will often recommend itself to publishers because they already know there's a fan-base and a way of selling that story-type. But I do agree with your finishing statement- you can add subtlety and originality to a stereotyped role by ensuring there are factors and motivations at play for the MC that make them 3D and different.
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