This is what separates the good players from the bad in GW2 and really really well in the engineer class. I am level 69 and am now getting the hang of what to do. I run pistol/pistol with the regular heal, grenade kit, flamethrower kit, elixer gun kit and the D-series defense golem. I've noticed that if you play smart you are GODLY in groups. For example, you have 3 blinds with this setup (number 3 or 4?) on the pistol/pistol, number 3 on the grenade kit, number 5 on the flamethrower. You have condition removal on the elixer gun (2 of them even), you have HoTs with elixer gun and it's F ability, you can buff with the regular heal F1 ability. Good damage in melee with flamethrower kit (does a crapton). Ranged AoE with grenade kit, ranged single target with pistols and you can debuff the enemy with elixer gun. I had specced into all power/precision but am now moving into +condition damage and +healing since I'm liking the support playstyle and with +condition your flamethrower wrecks mobs. I believe I'm 20/20/0/0/15 or so right now.
So here's what I do, oh man that guy is getting pounded while trying to rez: Knock back with flamethrower or toss a blind then help rez. Oh no, conditions on my whole party elixer gun to remove them all along with acid spray in case I miss. Quick debuff the boss with weakness from elixer gun, range blind with grenade kit, close range blind with flamethrower, toss out damage with flamethrower.
Now I'm sure all classes can do this but I don't see a lot of people actually doing it, maybe it's just different since with us switching it's so noticeable (like an ele) but it really goes a long way and makes dungeons so much easier when you are pulling out all the stops. I have a feeling once more people learn to play like this those crazy explorable dungeons will get easier. Hope this helps.