in Substance Painter you paint textures and more important: Materials! C4D Bodypaint only paints textures.
The second point is you paint your materials on the 3d Model until it looks good and on export you can generate the textures for whatever render engine you like. You have a game? Export PBR realtime textures for your specific engine. You render in Arnold a film? Export Arnold shader textures. You render in Redshift? Export Redshift textures. etc etc.
Substance Designer is a node based material generator. You design the materials there you later use in Subtance Painter.
It is a major workflow boost compared to classic texture painting because all shader maps are painted at the same time and you get immediate visual feedback how the material looks like in rendering while painting.
From Adobe standpoint it makes total sense to buy Allegorithmic. Because basically the Substance tools are nothing else but texture map generators/painters that often go hand in hand with Photoshop/Illustrator in production. Merging them would make complete sense. Let's see if they come up with a modeling software, too.
I wish MAXON would be more aggressive in buying apps for UVW, PBR texure painting tools, cloth sims, fluid and liquids etc. Because they are loosing massive ground on the traditional VFX field.