I'd still say he's a founder of Paypal just as much as Peter Thiel and Max Levchin were.

Elon is only founder of Tesla as an early investor and had direct influence in the company being named Tesla. The people credited with the actual founding had no business name and no money which means no business. They were literally knocking on the doors of billionaires begging for someone to make their idea a reality. Plus Elon also found J. B. Straubel who did the battery design. Martin Eberhard has EE expertise but not batteries AIUI which seems to fit his career trajectory if you look into it.