Reptopry

Yes, it is an error in the tool-tip.
Level 16 - 574
Level 17 - 585
Level 18 - 597
Level 19 - 609
Level 20 - 621

 

I would say Full Dexterity.
Being a dual wield class, you don't really struggle to get high Physical Attack combined with philo bonuses, you would benefit more from the extra critical hit damage, critical hit rate, and strike.
Also, there is a penalty for dual wield which I'm sure you're aware of, so Dexterity helps you counter the loss in critical hit rate.

Guard-Swordsman-Knight-Destroyer is for mostly Vitality stat players because of the Level 10 "Enhanced HP" Passive. This passive when max level gives you around 400 + 1% Bonus HP. In addition, you get an HP Recovery passive "Blood Leak."
Warrior-Swordsman-Knight-Destroyer loses the "Blood Leak" passive while maintaining the "Enhanced HP" passive, but only at level 5 meaning the Bonus HP is only 175+1% vs the 400+1% from Guard's Level 10.
 
Unless you are completely dedicated to playing Vitality Destroyer, I would just go with the general W-S-K-D Path, the differences only come from those two passives and they don't differ too much in stat bonuses.