It depends so much on the type of photography that you can't really quantify it in general...
Nature photography, street photography and sports photography have a fairly good-sized luck component, and a large experience/skill component too. Portrait photography has a lot less luck, and a lot more skill and lighting equipment. Wedding photography is a lot skill and a little luck (or absence of bad luck perhaps.) Product photography is almost pure skill, with some equipment...
Skill substitutes for equipment in many cases, equipment substitutes for skill in fewer cases, but probably more strongly in the cases where it does.
Well, I do motorsports so I agree with it being more luck than anything. For a race event (where I get 2000-4000 shots) I would say less than 5% of my pictures are salvageable and I really like less than 1-2% of them. Having good gear is nice, but it means nothing if you don't have the artistry, luck, and technique.
(This isn't meant to be personal, it just reminds me of something...)
I've always said you can tell a good photographer by the pictures they *don't* take.
I think it may be more indicative of the LF or MF stuff where you have to slow down and pay attention, but I find that if I'm in serious mode, I take a lot fewer shots because I know when I've got it- where I'll go to spray and pray in situations where I'm further from my comfort zone.
My number of salable images tend to be about the same either way, but the percentages change a lot.