The STR bonus, I believe, is only applied to base weapon atk. At least, according to the wiki's description.
EDIT: Also, the numbers are missing the over-upgrade bonus from the +5~+9 upgrade range.
So Thanatos would have 220 + 63 + (5~70). Because of the variance in over upgrade damage, it's easier to just take the median value of 7. So, it'd be 220 + 63 + 35 = 318.
Edited by mildcontempt, 10 November 2015 - 09:21 PM.