well, i don't know anything about gymnastics but I've not found isolation work do much for my barbell lifts or odd objects with the possible exception of the ab wheel.
I think it's the classic progression. when you're weak, everything makes you stronger, the further you progress, the more specialized everything becomes. In SM, really there are so many events to train that hit your core, hips and shoulders that the last thing you want or need is ab work per se. I think I have wasted too much energy on working specific parts of a movement or body in hopes it will get stronger when what I really need to do is work on technique, when your technique is flawless, you really only need a very few supplemental things in addition to the movement to get stronger.