There are people with already-hypermobile joints and tissue whose program is only stretching or yoga. There are people with extremely immobile joints and tissue whose program is only resistance. Both are making a strategic mistake.
Strength IS stability. Flexibility IS instability. The risk of chronic spinal and joint deterioration goes up with instability.
BUT, incredible power without the capacity to use it through full skeletal ranges raises risk of acute tweaks and strains.
So do both.
I’ve added this deficit Trx Sissy Squat (video here: https://www.instagram.com/p/BxPbI5Fhv17/ ) as a finisher after extremely heavy split stance and Hatfield squAt, and found I can go with increasingly greater ranges and depths AS my strength has exploded. As this extensibility has progressed, my recovery to train hard has improved. Don’t just play to one facet of fitness.