In an ideal world, each class would have different ways of engaging with each pillar of the game to accomplish similar or overlapping functional results.
To find a recently escaped villain, an arcane class would cast a spell like
Discern Location, a priestly class would rely on divine inspiration and/or intervention, an artificer would create small seeking drones, a social class would engage a group of irregulars and tap into the grapevine listening for whispers of detection, and a stand-up martial class would lead the hue and cry posse.
To survive the environs of the basalt castle floating in the lava lake, an arcane class would change his form to flame itself, a priestly class would call for immunity to fire, artificer would create a temporary and delicate exo-suit, a social class would have contacts capable of providing some defense, and the martial class would rely on scavenged material (magical or non-magical) to bolster himself.
To reach the cloud castle, the arcane class would cast
Fly, the priestly class would call for an apportation miracle, the artificer would craft wings from feathers and wax, the social class would have contacts to help, and the martial class would climb the mountain the cloud is drifting towards and leap across the gap at its narrowest point.
As it stands, D&D only really guarantees every class will support the combat pillar despite acknowledging the others.
*edit* Here's a link to a discussion from just before 5e was released discussing this topic.
http://www.enworld.org/forum/showth...d-a-fighter-versatile-out-of-combat-look-like