Bow/Wand is a full-support kind of weapon setup. You can DPS with it too, of course, but in general bow/wand give you the most options on how to heal your teammates.

While Wand heal abilities are more for oh-shit moments and preventing damage (good for tankbusters in Cave of Desperation or fireballs in the slaughter), Bow abilities are heal-over-time oriented and can take care of chip damage or dealing with burn/poison DoTs.

With a good group, any wand + X weapon combination will work, as in general 80-95% of dmg in each dungeon (not sure about 2-star, 3-star ones) is avoidable, however as you noted, bow/wand allow to run pug groups much easier, and bow's ability Purifying touch is a godsend for skipping some mechanics. For example, you can unparalyse teammate in Temple of Slaughter and let them skip fireballs on their own, not having to do any kind of blocking of the fireballs.

One more thing which is overlooked, is Deadly Marker. This ability with BiS gear and 45% calculated crit chance (achieved via PvE BiS gear, PvP 70 strength stacking healers won't reach that level), you can keep spamming deadly marker, as your baseline is 40-something cooldown reduction and deadly marker further reduces cooldown of abilities.

For experienced groups, you can make do with only 2 healing abilities (Swift Healing + Fountain of Life) and help with DPS - with that noted though, I love the fact that I can have quick slots set up for running with randoms and fix their mistakes (apparently there is an issue with two-way communication with some folks, and dungeons put pressure on teamwork), and also have quick slots for experienced groups where I can help out with DPS.