In the end its a simple economic calculaton:

Artstyle-To-Use must be choosen by:

(AverageTimePerAsset / NumberOfArtists) * NumberOfAssetsNeeded <= TimeAvailable

with: NumberOfArtists * MonthlyPay * TimeAvailable(Month) < Overall Budget

-> AverageTimePerAsset (smaller for Comic/Abstract look)(longer for realistic / detailed look)
-> NumberOfAssetsNeeded (should be estimated early by the Gamedesign planning)

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Thus, since Indy Devs have many more limits (often just one Artist, and also a limited Time - before Frustration stops the project)
they should either Choose a game where less Assets are needed
(Casual Games, Games where Assets can be repetatly used - like in a tilebased gameworld)
or use a quick-to-develop Artstyle (Comic / Stylized look with low details)