Hillary Clinton has made mistakes, just like any other human person, but she also does not get credit for the things she does accomplish. Powell might be overcritical of her, and he also has the tendancy to hold people to higher standards. It is also important to remember they are not on the same side politically.
She's helped first responders , worked for the Children's Defense Fund, helped create CHIP to which provides health care to more than 8 million children. She's human, so of course Hillary Clinton makes mistakes. But she's also very intelligent, driven and a hard worker. She's educated, supports LGBT rights and believes in equal pay, so no, she doesn't screw everything up.
Besides that Powell mainly attacks Clinton's personality in his leaked emails, it is highly unlikely that someone who has been a successful lawyer and has become one of two final presidential candidates could have "screwed everything up" in her career. Powell's claims that Clinton is "greedy" and has too much ambition would not only apply to most politicians -- perhaps even most successful people -- but would likely be considered grudging praise if applied to a male presidential candidate. It's not at all unusual to see critics point out ambition as a negative trait in women, but a positive one in men. Regardless of Clinton's potential suitability as president, Powell's comments are neither here nor there.
No, Powell's allegations that Clinton always screws up are unfounded. This controversy I believe relates to the email scandal involving Ms. Clinton. Ms. Clinton had explained to the media that she was unaware that she was violating protocol regarding the email messages that she had sent over to unsecure networks.