Hmm lets crunch some numbers, numbers solve everything. Class and skill of choice is the Shinobi’s Kunai x2, Clone x5 and spear lunge (with and without crits) for the sake of it we will assume clones all crit as well when calculating with crits, no other buffs other then spear lunge and finistra lvl 15 (+150 crit rate).
(damage is rounded up)
(Based on stat calculator max str is 585, max dex is 363)
(Max str gives you +579 crit attack, weight limit increase, Max dex gives you +357 crit rate, +357 evasion and accuracy)
Full Str Shinobi with crit: 790k damage
Full Str Shinobi without crit: 472k damage
(Chances of crit are low but finistra would make up for lost dex)
Full Dex Shinobi with crit: 560k damage
Full Dex Shinobi without crit: 335k damage
(643 Evasion, High crit rate with fin but losing 120k - 310k in dmg)
My suggestion is simple, go hybrid: Add 137 to str, 42 to con, 100 to dex. This would end up having the following:
Hybrid Shinobi with crit: 670k damage
Hybrid Shinobi without crit: 400k damage
283 crit attack, 178 crit rate (including 150 from finistra), +122 evasion and accuracy, added hp recovery, crit resistance and hp for survival.
TL:TR Go hybrid, or High str low dex, hoptile increases your crit chance. No matter what sword path you take i believe ALL your skills are largely influenced by Str.
(Edit, forgot to x5 on dex calculation, corrected)