I think fascinators are a very mixed bag. They’ve got to be exactly the right size to your head or the proportion is way off. If someone like Stephen Jones is fitting your fascinator it’ll look interesting and fit but they do not thrive off the rack. A hat is much easier to get right and they usually look much more sophisticated.
I usually love a hairband everyday but I don’t like a headband for formal events - it’s far too casual and can look like you are wearing a scaled up child’s outfit.
I want to express a small pet peeve of mine not necessarily at you but in general. Kate does not wear fascinators, she actually hasn't worn one since she got married. She wears mostly cocktail, percher and pillbox style hats along with hatband and boater style hat mostly. Most people place any hat that is not a standard hat under the category as a fascinator but they are many different styles and each with a specific name.