I do not agree. Like I said, Liberty is nice. The problem is that so is everything else. You're going to make exclusions.
Tradition and Liberty are both openers - early game policy trees. Picking two openers and thereby forsaking/postponing a different policy tree is, IMO, bad play (and something the AI does all the time, I'm afraid). Picking both Tradition and Liberty early means going both tall and wide at the same time thus not capitalizing fully on either. It is wiser to pick one of the openers, move on to Piety then suitable medieval policies (Patronage, Commerce) and finally into Freedom. Had I opened a cultural game with Tradition, I would almost certainly not pick Liberty as one of the five trees. In a late-game empire, Representation and Meritocracy are the only meaningful policies - everything else is obsolete. Adopting a full tree just for two policies isn't the way to go. There's much more bang for the buck to be had everywhere else at that point in the game. So, unless there's a very good case for not going Honor or whichever you're missing from Patronage/Commerce: no Liberty.
Liberty only truly shines in the early game. A free settler is immensely more valuable on turn 20 than turn 200. The same goes, to a lesser degree, for every other policy in that tree. Liberty becomes increasingly less valuable the further the game advances. The same is true of Tradition, but to a lesser degree. So, vice versa, by opening into Liberty I would most likely not come back for Tradition.
But once again, it is all highly situational. Playing France, I believe Liberty will be the 'correct' opening move in 90+% games, even if you're going cultural (thanks especially to the wonderful adjustments of the new patch which has fortunately done away with the rule that cultural victories are for small empires only). So I should correct myself on the line you quoted above because saying Tradition is better than Liberty for cultural isn't correct; it's just that the civs that are especially well geared for cultural victory (such as India) benefit a lot from Tradition.