profh0011 wrote:
"If Jack had attempted to leverage his offer from DC Comics with Goodman, perhaps he could have gotten a better deal from Marvel."

How likely was he to do that, when Perfect Film essentially told him, "SIGN THIS OR GET OUT" ?

What's the sense in Kirby signing anyway in 1972 after he got out? None.
So he's a poor negotiator. Even when someone tells you "sign this or get out" there is room for negotiation. To start with, since he was a freelancer and not an employee, "get out" had no meaning.