Comprehension.. I said core, not abs - your abdominals form part of your core group and there are a plethora of ways to engage them without crunching ๐คท๐ฟโโ๏ธ
Not necessarily.
To effectively hit your abs, spinal flexion is a must. That is what crunches are all about - spinal flexion.
The biomechanics is irreplaceable.