Abs and hip flexors tend to work in concert to lift the leg in a front extension, although it's the hip flexors and quads that actually do the lifting, with abs helping.
You definitely need core strength to direct anything in dance (let's just edit that to "....to direct anything."), so it's no wonder your Irish instructors were drilling you to build up your abs. Ab strength is the sine qua nihil of all movement.
And with regard to strength vs. flexibility, it is true that people who concentrate only on strength and do no stretching, tend to be less flexible; but this does not mean that the converse is necessarily true--that greater flexibility means less strength. The key is to build strength and flexibility in concert. If you are very strong, then you also should work to be flexible so that the muscle complementary to the muscle you're working can stretch far enough to work the working muscle through its fullest range of motion.
Often when people do teasers or similar exercises, they tend to "grip" with the thighs and hip flexors to "help" the movement. This actually is a waste of energy! It sounds to me, though, like your hip flexors need to be strengthened a bit. The flexors tend to be pretty weak relative to the rest of the body, although exercises like cycling and step, that bring the knee towards the chest repeatedly, strengthen the flexors quickly. In fact, many cyclists and steppers have very strong flexors! (Which also means they should be extra conscious of stretching them.)
Hope this helps.