just keeping things simple
the contribution of each point of HP vs each point of ATK to tiger cannon damage are equal;
ignoring gears(except weapon), buffs, and consumables, each VIT adds 1.25% HP (trans mod), while each STR contributes to statusATK (additively) and weaponATK [baseweaponATK * (STR/200)];
so STR would be contributing more as long as your weapon's base ATK is greater than 50 (which should be);
but because you already begin with larger amount of base HP (depends on character class and base level) than bare-handed ATK, and factoring in gears that increase by %, point by point, increasing maxHP is way easier than increasing ATK;
which is why one usually would end up with about 60,000 HP and only 1,500 ATK (including card damage modifiers) overall, more or less;
using the values above as a numerical limit, for the true maximum damage, ideally you want to have 30,750 HP and 30,750 ATK (half and half) - which would result in fantastic damage, but that is not going to happen;
you would think, you want to just prioritize increasing ATK with the best ATK increasing gears to "catch up" with the HP, but you may end up sacrificing equipment slots that could have added a lot of HP than the ATK you have gained (ignoring the sample limit values stated above), which may have been the better choice;
so in the end, it's better to just calculate it yourself with the all gears, buffs, consumables you have in mind;
a simplified tiger cannon damage formula (no combo modifier, ignoring the base level and SP contribution and minor bonus damage portions) is this: ATK * HP * (3/4000)
sorry if this reply didn't really help specifically (i could be wrong on some of the above ideas too since i simplified things);
Edited by ka10, 09 January 2015 - 11:53 AM.