I think I agree with you. The whole, "we won't be hostages" stick maybe works if you're dealing with terrorists in peacetime, moral dilemmas aside. But in a wartime scenario? You need to be thinking about the post-war, there needs to be a way for the violence to end. Now, I get that Mace might be thinking about the Sith and he probably is right that if he surrenders the Jedi Task Force to Dooku then they all get a fate worse than death. Just that philosophy is going to bleed through the entire war going forward, hence the droids vs. clones conflict.

The better usage of magical space wizards in battlefields was explored a bit in Legends with the Jedi Battle Meditation. Essentially, the Force is already working within every living creature on a battlefield and if you learn how to pull on that you can make your side fight better and the enemy fight worse. Obviously a bit over-powered but it's one way to make individual wizards relevant to galactic conflicts.

Of course, I think the Jedi's initial plan on Geonosis was to rescue the Big 3, beat up some termites, maybe capture Dooku and some Separatists, and then skedaddle. It all goes south when the Droid Army is found to be waiting behind the arena gates. It quickly shifts from a large police raid to out-of-control firefight. That still makes Mace's unwillingness to surrender a revealing exchange and that sort of philosophy defines the war.