I’ve seen suggestions over the years to use other applications, like mypaint, krita or whatever, for painting your pencil animations to get a better paint engine and brushes. This is of course a viable workflow but it is a little cumbersome. To start with image sequences are rendered frame by frame, you get one image for frame 1, one for frame 2, etc. while your animation can be on ones or twos, threes or fours or mixing them all differently across different layers leaving a lot of duplicate frames to paint.
That leads to my suggestion;
Export drawings instead of frames and do it on a layer basis.
If on layerA you have drawings on fr.1, 3, 6,7,8 then export a sequence named layerA_0001.png, layerA_0003.png, layerA_0006.png, layerA_0007.png, layerA_0008.png which you can import into any painting app.
You can choose to export current layer as a sequence or all layers as individual image sequences.
Likewise, you should of course be able to import sequences named this way and have them distributed across the frames accordingly.