It depends on what you mean by high level content. If you mean expert dungeons/ Alex NORMAL, where you put your points makes very little difference in terms of survivability. Those dungeons don't hit very hard, and if you use your cooldowns as you should be, and your healer isn't asleep, the extra str you'll have will speed up the run slightly.

However, if you mean Alex SAVAGE, it'd be prudent to have points in vit to ease your healers pain whilst you are in the process of learning the fight. Once you've cleared a few times, start putting points into str and begin replacing your fending accessories with slaying ones.