My Kargath M log being the only disc in the raid group (Ultraviolenz is my char name):
warcraftlogs.com/reports/B8AygzvRKXGtQwcq#type=healing&source=144
As you can see, I was 660 at the moment (663 now, so not much difference anyways).
I link that just to show you that you need to use PWS a lot more. Disc in kargath is extremely OP. Try to build up evangelism when you have time, and when Iron Bombers are raping your guild mates, just PI+Trinket (or save trinket for another round of debuffs, that's your choice) and SPAM PWS on the people with debuffs. You won't even let the other healers do shit, you will be absorbing everything. Make sure to start shielding as soon as the debuff is applied, or else you will waste some of that absorb.
Ofc there is another things you will be doing, such as Penance/cascade and that stuff. But I feel the most important thing is absorb as much Iron Bomb as you can.
I did overlook the other bosses, and your HPS seems OK. Maybe, in Brackenspore, you can find some time to CoW the rejuvenation mushroom; is really good if your tanks are fine, you will help the raid a lot.
I just want to emphazise that with a proper archangel usage you can boost your healling a ton. Look at this:
warcraftlogs.com/reports/mrYLzdgQcaJ2hX9M#type=healing&fight=34
I have almost 2 million more PWS than the other disc, and only 7 more casts. He also have 8 ilvl more than me. The thing is that I use Archangel better, and on top of that my PWS is doing 7% less overheal. That is because I choose better when and where to use it (I have a little bit more mastery too).
But don't worry, you are doing good.
To finish, I will give you some general things that I think will be usefull:
-Solace at CD (if the raid is not dying ofc haha)
-Track ability timers on bosses, so you can preshield a lot of people
-Track debuffs, so you can... guess what!
-Try to build up evangelism efficiently
-Penance is really good.
-A good PoH with Archangel 100% crit can do wonders (if you don't have mana issues)
-Remeber, you have more things than just PWS... but PWS is REALLY fucking good, so USE IT
-Get used to the "OMG, disci is so dumb. 1 button healer" from the others healers in the raid
Pd: I'm actually playing SP as main spec, so maybe there are things that I'm not doing good. So don't take all the things I said as THE things you have to be doing, just as tips
Pd2: I'm rly sry for my english, is not my language. But I hope you understand what I'm trying to say :P