The only downside to drawing on the iPad with a stylus is that you have to keep your hand and wrist off the screen, which can become uncomfortable for those artists that still draw with their wrist (which is something one ought to change anyway). Some apps claim to have wrist protection, but none of them are very good.
However, I know many artists do use the iPad and other tablets for creating art. They have changed their drawing habits and draw with their whole arm, and use the zoom feature to create detail they would normally create with their wrist touching the drawing surface.
I am not an artist, but I do enjoy drawing, and I found that a pen size stylus gives me the precision I prefer, and doesn't obscure much of the screen. I suspect the Cosmonaut would obscure more of the screen, being a thicker tool. This is something that is up to the user's preference, though - he might prefer a larger grip, or weight.
Be prepared to test out a dozen or more drawing apps. I found procreate meets my needs, but I also have several others, and each has merits to recommend it.