"Already more OP than White or Black Mage"...

We do ~10% less damage than BLM and have only one weak/expensive heal to compare to WHM's entire arsenal. The most "OP" thing we have is insta-raising, and even then we have no MP recovery tools of our own so doing so comes at significant cost to us. It's a stretch to say we even got BLM's Flare or WHM's Holy, since the spells we can cast resemble them in name only.
That's a very immature comparison.

That said, I will agree that giving us a Chaincast ability is completely unnecessary. Just adjust Dualcast so it can proc from a spell that has been Swiftcast and we'll have the same effect, three instants in a row where we won't just spam Jolt-Impact-Jolt-Impact after.