In FFXI SAM was brought in to be a tank.. Ninja was brought in to be a dps... It did not turn out that way.

If you take a close look at earlier FF series, you'll see that SAM actually is more of a tank. There are numerous threads regarding this matter on this forum. You'll find them.

I personally like to have another tank, one that tanks completely different than the current ones (maybe a parry/evasion tank).