I understand that's your aim. However, you're not the only one who uses your assets. Even for people who are going to go through the whole process in Blender, being able to get a good idea what things look like in MH makes things a lot easier than having to go through the whole process of exporting and then assigning materials--just to see if you like how something looks.
You're certainly right about the lighting, but baking can certainly be useful for materials that aren't reflective, and, in this particular case, except in extreme close-ups, no one is going to notice the difference with tiny pieces of jewelry. Heck, before today, I never even noticed the earrings lacked textures. Besides, who says no one is going to use these in a game?