Like many others, I would consider Joshua Tree and Achtung to be their best studio works. So, yeah, I guess they matched JT three-and-a-half years later.
In retrospect -- though it was also evident at the time, I suppose -- the general period of 1986 to 1992 was U2's peak in almost every way: commercially, artistically, musically, performance-wise, cultural relevance, etc. Though Rattle & Hum was a pompous, overblown film project (thanks Paul McGuinness), I maintain that if you strip it down to 9 or 10 studio tracks (and get rid of the cinematic release for the movie, which made the band look rather foolish) you have another studio album that's almost as good as JT or AB.
While there is a certain "pure" quality to their pre-JT work that I occasionally prefer (some of the sonic textures on Unforgettable Fire in particular are unique and wonderful), and while their "experimental" side obviously got a greater showcase circa 1993 to 1998, for me it is clear that roughly 1986 to 1992 was U2's peak.
So, Bono was both right and wrong. They were just into their peak period when he said that... they wouldn't beat it, but they did match it.
