What in Gods name would you want a Sentinel with 10 INT!!!! Sentinel main advantage is skills you know! If you are gonna use a sentinel at least put it at 12 or ideally 14 INT....
Well, as the bonus from being a Sentinel and the bonus from having INT don't multiply together, it's not necessary to do both. The point of being a Sentinel and the point of having INT are almost the same. Maybe he's not a retard, and knows that he doesn't need 400 stat points. After all, most skills can be used by most other party members most of the time. I focus on the skills I can't use other people for, and maybe the ones that I occasionally am alone for, and leave the rest to, say, other Sentinels.
