Is more flexibility always better in yoga?
No. Yoga does not ask us to become as flexible as possible. It asks for a body that can participate in practice with stability, freedom and awareness. Some practitioners naturally have large ranges of motion and actually need more strength and control rather than more stretching.
A posture is not improved merely because it becomes deeper. If depth causes the joints to lose support or the breath to become strained, the visible shape may have increased while the quality of yoga has decreased.
Think of mobility and stability as partners. The freedom to move is valuable, and so is the capacity to control that movement. A mature practice cultivates both.