Which is exactly my point: if we're resorting to external assets, there are infinitely more spritesheets available online for the low, low price of free, because making decent sprites is such a comparatively small effort that even artists themselves attach less value to the task.
(Which still isn't to devalue the effort that it takes to make good-looking sprites; I've tried, and damn do I suck at it.)
You need a baseline of art, and then you need to tweak the animations to match your video game. A model may not have a "double-jump" animation but you can easily add one through bone manipulations with any 3d model.
But if a sprite-sheet were missing the double-jump animation? You're either doing it yourself (hard pixel art style) or hiring someone else to do it.
(Which still isn't to devalue the effort that it takes to make good-looking sprites; I've tried, and damn do I suck at it.)