There are several problems in that last sentence:
A) Only 20% of All You Need Is Love consists of The Beatles' own words (The Beatles being Paul, George, and Ringo, but not John). The other words are supplied by Yoko Ono, Cynthia Lennon, Pattie Boyd, Maureen Starkey, Derek Taylor, Neil Aspinall, "Magic" Alex Mardas, and twenty or so others in or around The Beatles' circle.
B) All You Need Is Love is not an oral history. An oral history interweaves carefully selected quotations and anecdotes from numerous sources to tell a chronological story. All You Need Is Love is a collection of unedited transcribed interviews, complete with every "uh" and "um."
C) All You Need Is Love is not a landmark anything. A landmark marks a turning point, and a landmark book introduces new information that might make readers rethink its topic. Brown and Gaines conducted the interviews in All You Need Is Love 44 years ago for their The Love You Make, a biography of The Beatles often criticized for its salaciousness and historical inaccuracies. The surviving Beatles apparently felt their former associate Brown had betrayed them upon its publication.
This does not mean that All You Need Is Love does not have some value for those who are willing to slink back to Brown and Gaines's corner table, although that value is not necessarily a more complete understanding of Beatles history. In some ways, All You Need Is Love reveals more about its authors than its subjects. By unveiling the questions Brown and Gaines asked of their interview subjects back in 1980, All You Need Is Love clarifies the two authors' goals when writing The Love You Make . A reader might assume that it was so scandalous because this was the story that naturally emerged the deeper its writers delved into The Beatles' lives, but they were clearly determined to tell such a story from the get go. They quizzed their subjects on dirty business dealings, interpersonal conflicts, the Maharishi folly, the disastrous Manilla trip of 1966, The Beatles' sex lives and drug use, and Brian Epstein's sexuality and the circumstances of his death almost exclusively. They were also fixated on the scene at the Ad Lib club for some reason.
Brown and Gaines had zero interest in The Beatles' creativity. They often asked leading questions, though it's refreshing to see how infrequently their interview subjects rose to the bait. DJ Bob Wooler, whom the authors allege that Lennon beat up, hilariously takes them to task for such questions and even has the guts to ask Brown if he thinks he'll still be friends with The Beatles after publishing the book. Brown's sheepishly noncommittal response is pretty hilarious too.
We also learn how their subjects reacted to such provocative lines of questioning. Paul is open and honest and seemingly determined to get things off his chest a decade after the deterioration of his band. Ringo is generally open and cordial but has lines he won't cross. He never insults anyone and immediately shuts Gaines down when asked to talk about LSD. George belies his "quite one" reputation by responding to the slightest question with extended riffs on the topics that most interested him: spirituality, India, and confessing his privileges. Perhaps the most fascinating interview subject is Yoko Ono, who is surprisingly complimentary of and sympathetic toward Cynthia Lennon and clearly understands how she wronged Lennon's first wife.
That kind of empathy is often lost on the authors. Brown's introduction further emphasizes his agenda by recapping some of the ugliest assertions from The Love You Make with a curious lack of self-awareness. Gaines displays startling insensitivity when interviewing Brian Epstein's mother. The authors sometimes personally insult subjects-- such as Yoko, George, Vic Lewis, and Alex Mardas (who, one must admit, does not present himself very well)-- in the brief commentaries that introduce each interview. The book generally lacks organization and sometimes lacks orientation. A two-page commentary from Brian Epstein, recorded in 1966, will bewilder anyone who does not already know that Maureen Cleave was the reporter to whom John made his "bigger than Jesus" comments. Despite certain merits, All You Need Is Love remains a tough book to defend and an impossible one to love.