He is most certainly a Barca legend regardless of what others say, came in and kicked out Rustu who was still a decent GK back then and also ensured that we had a good reliable GK for the first time since Zubi had left us.
Nothing of this makes him a ''great'' GK.
As for the whole benefiting from a great side where he had to make very few shots per game is completely BS in my opinion, it is way easier to be concentrating and making saves when you are under pressure throughout the game but a whole lot harder when you have little or nothing to do and then suddenly have to spring into action from a counter attack etc
Barcelona under Pep Guardiola was usually that dominant that Valdes wasn't under any sort of real pressure, especially with defending set-pieces. Guardiola developed a great tactics to minimize dangers of having short players and trash GK in terms of dealing with football when in air. His ONLY job was basically saving a 1 on 1 chance from time to time and it's not like Barca were giving a lot of those. We've seen what are his real qualities when teams actually started to dominatee Barcelona this past season. Can't rush from his goal line to save his life, tends to let in A LOT of soft goals and is often out of his position, can't play with his legs very well for shit despite some Barca fans claiming it's his greatest quality.
As I said, you'll see how good Valdes actually is once he is out of Barcelona and playing for some lower level club because there is no way any serious CL contender will come for him.