I've been trying to like the Chanter and make it useful but so far I'm failing (PotD, sometimes Ironman). Considering that I lack experience I am not going to make any claims but merely gonna post my observations.
In PotD (especially Ironman) Chanter seems a liability. 15 seconds is a loooooong time (and that's if using short phrases). The battles in this game are very fast. First few seconds seem crucial. But with a Chanter the team is a man down first cca 15 seconds. That's insane. It means others lose health and endurance more than they would if they had actual support from the first second, which then either increases the frequency of Rests or the chance of defeat. When people in the forum complained about Chanter being slow I thought it could be they just like faster battles on Normal non-Ironman difficulty. So in a way, Chanter would be like a Mesmer in GW1 PvE (Prophecies) - by the time it can actually do anything elementalists blow the place up with AoE's. However, after actually trying the Chanter and playing this game, I realize there's some truth in that. Battles are really fast. If you position your tank and block the door then yeah, no problem, but in this case you win even without the Chanter. There's something else that's important: time. Time is money as they say. Chanters make battles slower. So you might as well just burn the per-rest spells and abilities, and then travel where you can Rest. It's probably going to take about the same time as making Chanter useful.
One thing that worked for me was making 4 Chanters and then in the open areas (first few levels) I would start a combat, retreat (while maintaining combat active) and assail the enemy once I had Invocations ready. This makes battles take longer but is probably safer as long as you can run away. My problem here (other that boredom and repetitiveness) was that I had Phantom summon (which seemed really awesome) and when I ran into those Boars the Phantoms died quickly and couldn't hit anything (PotD Ironman) which wiped out my whole party because other than the summon Chanters were freakin useless so when the summon did not work neither did the class. (Of course, I learned not to put all the eggs in one basket.) Related to that, I've been testing Thunder invocation with Kana, and that's even more disappointing. This invocation almost always misses so you can imagine how happy I am waiting for 15sec to do something and then seeing "missed". That's a huge gamble I don't think gambling works in PotD Ironman.
Lack of burst. This could, I suppose, be fixed with scrolls. Or maybe making the Chanter a tank or off-tank.
Placement. He has to be closer to the frontline which means he's more likely to die, and if he's more back it means his chants are not covering the front. If he's in the middle he is also blocking possible Druid spells for example, and from what I've seen Druid does so much more (although it's rest-limited).
Most of the chants are highly situational. If a chant only helps 1-2 allies engaged in combat, then it doesn't help the other 4-5 and you might as well go with Priest or something. If it debuffs enemies then it's either going to take a while to see any difference (endurance loss) or the chance will be only relevant for 1-2 enemies (with certain damage type) while others are unaffected. And while I do lack experience in this game (as I said) the numbers on paper just don't seem so great. I get the idea of "a bit of everything" class, but I'm afraid in combat what helps is a tank who is nothing but the tank, which is why people use 1-2 tanks and not 3 semi-tanks semi-melee damage dealers.
I really like the names of Chants and Invocations and would like to have a Chanter in the party because I've always liked more unorthodox classes. But I need something that works. I've tried ranged Chanter, tank, and off-tank and wasn't satisfied with either. This is only first few levels. But what scares me is that Chanter doesn't seem to level well. Higher phrases are longer, so it means less Invocations (while other classes get more spells and abilities).
Advice is welcome on any kind of Chanter that works because right now I'm about to give up on this class, especially considering that half of the nerfs in new patch are intended for the Chanter.