Combat-wise, sure, she's the last, but you can't expect a medical-nin to excel in combat like the past Hokage did. Not only is that retarded, it's an unfair comparison .-. It's like comparing a doctor to a soldier in battle. No shit the soldier is going to win, he specializes in combat. But the doctor can be just as vital in a battle as the soldier.
Not to mention the fact Tsunade has monster strength next to her huge durability. Her intelligence is most renowned as the best in the world for her expertise in all areas of medicine. She has been credited with creating the official Medical-nin system and the laws that govern them. Saying she sucks... have you been paying attention to the manga at all?
She may be the least effective Hokage in combat, but otherwise she's a perfectly capable leader. To put it bluntly, the only thing that sucks here is your thread. Not Tsunade.