The "what if's" are nice for chatting about but nothing more.

Bradford simply can't stay healthy. It has always been his downfall. He doesn't have to take a brutal hit to be hurt; just stepping wrong can do it.

And staying healthy is right there with how well you play because if you can't get on the field, then you can't help the team.

But I'll add one more thing: Bradford is not a risk taker. There's a reason he's known for being Checkdown Charlie. For some coaches, like Fisher, that is exactly what they want. For other coaches like Martz, no way. And for McVay, never. Martz and McVay are aggressive and risk takers so they need a QB with a risk taking mentality. QB and HC and OC need to match in their views and game mentality.

I doubt Martz would have much liked Bradford. McVay wouldn't want him for that reason.
McVay fits with Goff because Goff is a natural risk taker and likes to throw down the field at every opportunity. And (fingers crossed) Goff has a history of being rag-dolled and thumped and some how or another he gets back up.

Why that is so different for different people I don't know.