I realize there are instances where kaiju are shown to get tired. And I would argue that all the examples you cited are more cases of monsters being injured than fatigued. The vast majority of films do not depict giant monsters growing weary from fighting one another. That's a very human thing that happens and why it makes sense in wrestling, MMA, boxing games, and sports games in general, but not so much a giant monster fighting game. Regardless, I think we both agree Defense is an intriguing idea!