Any artist who makes a living on their art cares about market share- at least to the extent that they have to go back to having a day job if the market share gets low enough.
Incorrect. They have to go back to their day job if their sales get low enough. If selling 1,000 units a year in a market of 10,000 units a year is enough, they don't suddenly starve if the market expands around them but they don't and now they're selling 1,000 units a year in a market of 100,000.
I see your point and you are both correct and incorrect. It's true that an indie artist who needs to sell, say, 5,000 comics a year doesn't have to care about market share as long as they can support themselves with the sales of 5,000 comics.
But it's also true that if you are the lowest rated comic published by Disney, you'll probably be cancelled regardless of gross sales numbers. If all the other books start outselling you, Disney probably won't consider staying in business with you worth their time.
And if you are fired by Disney, you may find yourself in need of a day job.
