It looks very plausible that stretching before you exercise doesn’t do much for you. Multiple older surveys suggested this.
Annoyingly, the studies linked in the previous paragraph are 2 decades old, and somehow I can’t find a large, well controlled, trial.
Only up to a point. Hyper-flexibility, especially of hinge joints, actually causes injury frequently.
I have hyper-flexibility, and I hurt myself quite a lot because there’s just no resistance to the movement until it’s too late in many parts of my body. I also have to be very careful with my elbows because they bend backward about 15 degrees, and so could very easily be snapped by a forceful impact when fully extended.