Is that why each time Ulfric makes a decision he sounds like a cowardly indecisive person who relies on Galmar to make decisions for him? Is that why he's willing to challenge a kid to a duel but not the Jarl of Whiterun? Is that why is surrendered without a fight in the beginning?
Well, first of all, Ulfric actually cares about the people of Skyrim and understands that the decisions he has to make are not always pleasant ones. If he was so gung-ho to go through and kill tons of soldiers to retake Whiterun you'd probably call him an evil bastard. Galmar just wants to kill everything. Ulfric understands that that is stupid, and he doesn't take the sacrifice of soldiers lightly. He doesn't NEED Galmar to make those decisions, but he recognizes that they aren't easy to make, at least not for someone who isn't an evil bastard. Which is why he asked Balgruuf to ally with him in the first place.
As for the Jarl of Whiterun, it was explained why he did that. He had already shown that he personally was strong, and he needed then to prove the might of his army.
Just because someone is strong does not mean they should operate with half a brain. This is what makes Ulfric such a strong leader, because he knows the consequences of his actions and while he is willing to make tough decisions, he actually thinks about what is best for the people and respects those who fight both for him and against him.
I don't know why he surrendered without a fight in the beginning. But I do know that if you join the Imperial's side, he doesn't make that mistake again... unlike General Tullius, who sits on a bench and whines because he's losing.