what struggles did Warner have in the Arena League?
The struggles he had in the NFL were due to breaking his hand and not being able to grip the ball. That plagued him from '02 - '06 until he started wearing the diamond handler gloves. Some argue that he just needed time to heal but the evidence doesn't support that idea. If he was "healed" after 4 years, then it stands to reason that he would have stopped wearing the gloves at some point. Which he never did. Even in off the field activities he would wear the gloves while throwing.
So, does Goff have some physical limitation that we don't know about? Because that's the only way I see Goff's struggles resembling Warner's struggles.