Yeah, they should give Cooper Flagg a few more seasons before we really see his potential. The problem with being a 1st pick is the high expectations, especially if that pick was hyped even before the draft. We shouldn’t judge based on draft or summer league performances alone. Sometimes, there are players who perform well in the summer league or even in their rookie season, but end up getting washed later on.
You're right that the average rookie needs a few seasons to get used to it and reach his full potential. However, it's worth noting that there have been several cases in NBA history when players selected with the first pick were frankly weak, i.e., didn't show the results that were expected of them.