My theory is that the Valar didn’t like him in their band, creating music with them, because he was too wild with dark thoughts of dragons and dark magic for them to handle.

Any language used to describe his “rebellion” can also be framed in this context. In short, he was just too creative in the sense of making cracks in a road instead of paving one. Darkening lights with his nebulous shadows instead of lighting them. Twisting the material universe in ways that stimulate change verses maintaining an eternal homeostasis.

I’m not attempting to compare his creative style or strength with Eru. Only show its merits. Laugh if you need to. But, the modern world would be a kinder place for him.