You're allowing your personal feelings for Musk to interfere with facts. Musk provided money, design, and leadership at critical early stages of the company. He's obviously a founder and you are simply wrong for disputing that.
It sounds like he was an influential early investor, but the situation you've described isn't what I would typically think of as "founding" a company. I'm surely not alone in this, thus the present debate. This isn't to diminish Musk's huge influence either; but folks tend not to love when the meanings of words are changed for PR.