As a mithra with 5/5 STR merits i got 141 (base+merits, Hasso, mithkabob). Elvaan got 8 more base STR and Taru 3 less than a mithra as far as I know, so there is your difference. However with standard gear you should be able to break 1k frequently depending on the mob.
The more aggressive you play the more dmg you'll do and in most cases it is allright to do so, even more if you're backed up by some competent healers, who don't sit an on their MP.
I don't intend to boast but as of now I have met about 2 or 3 other SAMs playing as aggressively as I do, not saying the others had bad gear or merits or anything like that, but the difference between an aggressive and a defensive stance is pretty big.