I agree with Jalim on this. Infiltrate is shocking. Advanced picklock > Infiltrate. If you search hard enough there is a post by Zulg on this topic that orders the effectiveness of opening locks.

Advanced picklock is highly disappointing now since they nerfed it several years ago. Nowdays all the actual doors/containers you take advanced picklock to actually pick, you can't.

Having said all that; since you are wanting a PvE explorer definitely take mystic path up to at LEAST glimpse. Glimpse is probably my favourite thief skill now since the advanced picklock nerf. Put points into gentlewalk, shield block and shadow disappear as well.