Yeah, Phantom Thief gains a fair bit out-of-combat, but you give up sneak attack (and debilitating strike) and don't really get anything which compensates directly.

Unchained you at least get Dex to damage if you go melee.

Gang Up is especially not worth it losing the sneak, by the way. If there is anything to make use of your higher skills (like 3.5's Knowledge Devotion) that would be more appropriate. There may be some fun to be had with Vigilante talents, perhaps using Extra Talent.