More mobility is not better, per se. Ranges of motion are going to be individual to each person but there is definitely a middle ground between less than optimal and more than optimal.
People tend to acknowledge that less than optimal mobility is an issue and it is.
But more than optimal is often ignored. The problem arises here when there is too many range of motion and flexibility but not enough stability. Movement wise we categorize this as hypermobility aka too much mobility. In this case, there is a lot of stability, which is problematic.
Similarly problematic comparing to lacking mobility, just on the other end of the spectrum. Both of them need addressed for optimal function and injury prevention. More isn't better, better is better.
The following is an interesting example. The first (Chase) is an example of less than average mobility on this exercise. The second (London Danny) is average or a little above average, but needs stability to prevent the cramping, which tends to happen. (He was a little dramatic ;) ) and the third (Tiki) is an example of hypermobile range of motion in which we would work on controlling range of motion / flexibility / mobility with end range stability.