I have been performing crunches for the last year with 20kg plates; mainly because crunches are supposed to be superior to situps.
However the other day I did decline full range situps with the same 20kg and while I didn't feel much difference in the burn the following 2 days my midsection felt like it'd gone a full 12 rounds with a heavyweight boxer. I could feel the entire length of my rectus abdominis from sternum right down to the bottom near my pubic bone.
Now I know that the psoas perform much of the work past the initial crunch and you can certainly feel the majority of the pain in full range weighted situps in those muscles but the DOMS I felt for the 2 days after that workout seem to suggest that the full range situp worked my abs if not in a better way, then in a different way.
Personally, I doubt the common belief that DOMS doesn't indicate microtearing and rebuilding of muscle fibers and so I think, again my opinion, that these full range situps work better or at least did for that workout, then my usual crunches.
Am I wrong? missing something crucial here (maybe my crunches haven't been full range) or is the 'crunches better then full range situps' another myth of BB?
That may not be the case. You may experience severe DOMS because you just switched to doing sit ups. May be because your abs was hit from a different ROM. Your best bet would be to mix your abs workout, do both full ROM and partial ROM.