I believe the prophecies make that clear. They mention only Callandor, and never mention the choedan kal, which are much stronger. Callandor must have some property besides pure strength which makes it valuable. It can stop balefire after all, so it clearly has some important unknown properties.

I don't believe Callandor is flawed. It was made in the Age of Legends, at the height of AS strength by AS who knew exponentially more than anybody in Randland. Could they really have "forgotten" something as fundamental as a buffer? Sometime so basic that even the most minor angreals have it? I don't think so. Therefore I think that any properties it has must be intentional.

Perhaps Callandor is a sa'angreal for the True Power. Perhaps that is why it seems to "magnify" the taint, since the taint is of the DO and the true power is also of the DO.

If two men and one women can make a three-sided link, then Rand could channel the true power, the other male channeler could channel saidin, and nynaeve could channel saidar. Alternatively, maybe Rand could channel both the TP and saidin at the same time (not sure if that's possible) and two female channelers could both channel saidar to balance him. Not sure how it will work out in the end, but I think Callandor still has some secrets left to unravel.