I promise to go into the book itself, but let me first mention the premise of the other part -- what do historians think about the competence of the CIA -- is tough the same way "let's rank all the American presidents" can be -- by what criterion?

In the Congo, in September 1960, the station chief (Larry Devlin) received a message that someone from "Joe from Paris" would arrive with a mission. "Joe" (chemist Sidney Gottlieb, more famously the mastermind of MKULTRA) came a week later, with a special poison meant to produce a disease local to Congo. The poison was designated for recently-elected (and perceived Soviet-leaning) Patrice Lumumba, suggesting it should be put in his food or toothpaste. Devlin asked who had authorized the operation; "Joe" claimed it was President Eisenhower. (Eisenhower had indeed said something to CIA Director Dulles about "getting rid of Lumumba" but whether this meant literal assassination is up for debate; the important thing is it got interpreted that way.)

Thinking the idea was generally harebrained, the chief stalled for months and eventually nixed the plan, and the assassination didn't go forward. Not long after, in 1961, Lumumba was shot by a group supported by the Belgians and led by a Belgian mercenary.

Does that mean the Belgians were more competent than the US? Keep in mind also the US helped opposition groups -- including the eventual execution squad -- financially and and with intelligence and clearly were not sad to see Lumumba go.

This story could be (and has been) painted in myriad ways, but the "death by toothpaste" has often been zoomed in on for the comedic element. With "success" simply meaning the murder being finished, the US could be painted as both incompetent (with the aborted plan, and waffling CIA) and competent (paying the right groups for the deed to eventually be done). And then there's the "morality metric", supposing we essentially do the opposite and judge every assassination as a negative strike against an intelligence agency -- by what value do we quantify Devlin's refusal to go along with the original plot, and what about the fact (in between the toothpaste incident and the final firing squad) Lumumba later ordered a military action (involving secessionists) where civilians were massacred? (The UN Secretary General called it "incipient genocide".)

There isn't an easy way to "score" all the events above, and it's easy to tell the story without falsehood that nonetheless slants a particular narrative either way.

Additionally, keep in mind many things are still classified in all agencies, and not every country has a Freedom of Information Act (nor necessarily a flurry of governmental investigations in the 1970s that brought some of the dirtier tricks to light) so just trying to line up historical deeds isn't an apples to apples comparison. It's safe to say the US was stronger in technology, and the Soviets were stronger with HUMINT. Even that requires some judgment calls in terms of "quality" since the US had a much more open society that was easier to infiltrate to begin with.

...

Having said all that, let's turn to the Weiner book. It has serious problems right from the title premise, involving a supposed exchange between Dulles and Eisenhower. The book presents a long speech by Dulles, with the response:

At the last, Dwight Eisenhower exploded in anger and frustration. “The structure of our intelligence organization is faulty,” he told Dulles. It makes no sense, it has to be reorganized, and we should have done it long ago. Nothing had changed since Pearl Harbor. “I have suffered an eight-year defeat on this,” said the president of the United States. He said he would “leave a legacy of ashes” to his successor.

Weiner tries to paint this as frustration with the CIA. This is an entirely made-up dialogue, and the "legacy of ashes" line from Eisenhower was in regard to military intelligence, not the CIA.

I don't really want to slog through point by point, but there's cherry picking and downplaying aplenty to give the right slant. Any successes are downplayed or omitted. In the book, Weiner paints the U-2 spyplane as a failure, because it was an adaption to not having enough HUMINT, and somehow that meant the adaptation was a failure. The CIA successfully predicted the Rwanda genocide of 1994, which Weiner gives as a failure. ("No one listened.")

Weiner brings up the Congo (in the section titled 'To Avoid Another Cuba'), but leaves out all context (and of course, the "incipient genocide") and somehow simplifies the situation down to an overwhelming power move rather than a complex geopolitical situation, focusing on simply the badness of the replacement of Mobutu (who was indeed quite terrible). Of course, it is possible Lumumba's ordering of "incipient genocide" might not have turned into full genocide, but from the perspective of people making decisions at the time it was impossible to know. (It must also be added, again, the assassination plot started before the massacre, among those worried about the Soviet presence -- so the US doesn't come out as pure either.)

I cannot recommend the book, and in my literature search I haven't found any academic historians who recommend it. It reads like the author had a thesis and gathered only evidence that supported it, without considering the full context of history.

....

Bring, O. (2011). Dag Hammarskjöld's approach to the United Nations and international law. Estudios Internacionales, 44(170), 159-172.

Johnson, L. K., & Jeffreys-Jones, R. (2008). Tim Weiner’sLegacy of Ashes: The History of the CIA. Intelligence and National Security, 23(6), 878–891. doi:10.1080/02684520802591475 (Read this, if you want a serious review in a research journal, which rightly points out the book only makes bare reference to any of the serious scholars in the field.)

Kalb, M., Kalb, M. G. (1982). The Congo cables : the cold war in Africa--from Eisenhower to Kennedy. New York: Macmillan. (This is out-of-date and there have been new documents including the 21st century, but is still the most readable narrative about what happened in the Congo.)