Luo's comments reflect a widely held view among civil society and Western states that Bachelet, a former Chilean president, has been too soft on some governments when they are backsliding on human rights around the world.
However, they welcomed the release on her last day of a report on the Xinjiang region which said China's "arbitrary and discriminatory detention" of Uyghurs and other Muslims may constitute crimes against humanity.
"We are mostly disappointed and expected her to be firmer on China overall; however leaving with this report helps her office's credibility," said Zumretay Arkin, spokesperson for the World Uyghur Congress.
Bachelet had earlier said she has been under "tremendous pressure" both to publish and not to publish, with Beijing asking her to bury it.
China, which vigorously denies any allegations of wrongdoing in Xinjiang, wrote a 131-page response to the report, which its mission in Geneva described as a "farce". On Ding's case, China's foreign ministry said it is a country governed by the rule of law, and everyone is equal before the law.
Bachelet's critics hope her retirement on Wednesday will mark a fresh start. "We are looking for somebody who is willing to speak out in a principled way, regardless of the perpetrator," said Human Rights Watch head Kenneth Roth.
However, her defenders say her political skills won her access, such as the first trip by a high commissioner to China since 2005 and a deal to bring monitors to Venezuela. They also praised her attacks on systemic racism and commitment to new environmental rights.
Bachelet defended her approach to the job. "Constructive engagement creates the space for criticism to be acknowledged and acted upon, to ultimately help make a difference in people’s lives on the ground," she said on Thursday.
Not for the weak
The battle over Bachelet's legacy embodies the political tensions between more liberal and conservative countries over human rights arising in the choice of successor.
The process is under way but a void is now certain with Deputy High Commissioner Nada Al-Nashif stepping in temporarily.
It is up to UN Secretary-General Antonio Guterres to make the appointment which then needs to be confirmed by the General Assembly. The roughly 10 potential candidates include UN official Volker Türk of Austria, career diplomat Federico Villegas from Argentina, and Senegal's Adama Dieng, who previously advised Guterres on genocide prevention, UN sources and diplomats said.
They say China and Russia, both powerful permanent Security Council members, will favour a politically minded successor, indicating a possible battle ahead.
"Western states and NGOs are pushing for a human rights advocate but a global policeman would be unacceptable to China, Russia and many developing countries," said Marc Limon, executive director of Universal Rights Group.
If a choice is made quickly, one of the first challenges will be addressing the next meeting of the Geneva-based Human Rights Council starting on Sept. 12, set to discuss possible Ukraine war crimes.
The body's decisions, while not legally binding, carry political weight and it can authorise investigations.
There have been recent hard-fought debates over sexual rights as well as the Yemen war amid growing signs that absolute monarchies and autocracies are gaining influence.
Limon said another politician from a developing country could help bridge the differences. But for others, like Bachelet's vocal predecessor, Zeid Ra'ad al-Hussein, there is only one way to do the job.
"My hope is that her successor will be strong, independent-minded, not easily intimidated by anyone," he told Reuters. "I would say: don't do it if you are going to be weak."