I have a problem with this line of thinking.
One thing is to say Hanging leg raises provide a better workout for your core/abs. So much is true. But saying or implying that crunches should be avoided or dismissed alltogether seems to go against many sources that list them as a primary exercises for abs. I think there is a time and place for crunches. If they were truly pointless, I think the fitness world and science would have dismissed them long ago.
I think they are a good option for those who lack strength to lift themselves hanging from a bar, I see several guys really, really struggling to lift the legs, it is not an easy move you can get into on a whim, let alone do sets and reps.... they'd be better off doing crunches, if they want to train abs in an isolated way, specially if they are more into bodyweight/calisthenics, aka they don't "train properly" to exercise their core/abs with squats and deadlifts.
and I am really not sure what to think about the "it hurts your back" line. The way I see it, if you do them wrong or don't have the strength to activate the ab muscles when doing the crunches, your body will start to try to get help from other parts, particularly neck and back, something that really shouldn't be happening. Any exercise done wrong has the potential to be dangerous...but maybe crunches are a different thing and I haven't read enough about them and indeed, they hurt the back, regardless of whether they are being done right or wrong, so who knows. I can tell from my experience that they don't hurt my back, ever, when I first started doing them yeah, I'd feel back and neck sore because I sucked at doing them, but that was the first or 2nd week from when I started doing them.
and in my own personal opinion and experience, (maybe science disagrees and that's o.k), I have seen better results from crunches than from planks.
one thing we can agree on is that Hanging leg raises are the best choice.
