Touching your toes doesn't fix your backswing. Flexibility is passive range — how far you can be stretched. Mobility is usable range — how far you can move with control, under load, at speed.
Golf runs on mobility: ankles, hips, thoracic spine, shoulders, wrists. Train movement you can own — controlled rotations, progressive swings, strength through range. That's the range of motion that shows up at impact.