Hey Sunnae, and sorry for the long response time.
First of all, you’re fighting with the strongest proactive healers and when done properly they will snipe pretty much all damage going in. Overhealing is quite a big deal.
I checked your amory and saw that you are running with the leech trinket. This is a natural enemy for a healer’s ability to produce raw healing. The total amount of leech done on some pulls are upwards of 10m (although you can’t take credit for all of it due to some natural occurrence on gear).
Okay now let’s start, Riptide is decent although slightly inconsistent ranging from being cast every 7-8.5 seconds. Keeping it on cooldown is important in order to utilize our 2p properly and it will even further increase the value of High Tide. The amount of hits from Chain Heal is a bit low when you’re running with High Tide, it should at least be 5+ while your’s is slightly below.
Healing Stream Totem needs a lot more attention, you use it on average with a minute apart the casts, resulting in only getting half the benefit it has to offer (which is a lot). Upping this could potentially increase healing of HST alone by 100%. It’s just ‘fire and forget’ and then it’ll do all the work.
I can see that you bascially use Unleash Life on cooldown. To put it mildly, this spell is only valuable when you have to alter your position. Looking at the replay I can spot a few casts that were unnecessary. Any other heal we have gives higher HPS than UL when people are below 100% hp, even when considering the increase on our next heal.
Then Spiritwalker’s Grace is cast on average once pr. pull (looking at fights lasting longer than 5 minutes), if I am to assume that you use the glyph so you can cast it more frequently (every minute), then a single cast on 5 minutes is low. This especially when looking at an encounter like Archimonde where movement is required often.
You could be a lot more aggressive with how you spend your mana. This is how I view Archimonde, you should essentially be OOM when entering phase 3 and then use the channeled mana pot to regain mana. This amount should then last you throughout the phase until the boss has been defeated. You only really need healing for when the infernals spawn, which you should have cooldowns assigned for.
Another idea might be swapping your weapon enchant for the one that procs mastery, the spirit enchant nets you an average of ~170 spirit while the mastery enchant’s average is ~230.
Elemental Blast could use a bit of love, you have 17.2% uptime at most and 8% as the least. There definitely is a love/hate relation to this spell, and the time you save not casting it can be spend on heals. The only problem here is that the time you spend not casting this is mana wasted. This is something you have to feel around.
Ascendance seems to be missing from some pulls and on those you used it, it wasn’t able to output a lot. Cooldowns should be used early on in the fight and then as often as seemingly possible. Your paladin pops his wings on cooldown from the first time he uses it, allowing for him to get the most benefit from it. On one occasion you pop Ascendance right as he uses Wings. When using Ascendance just try and stand still for the full duration and get as many Chain Heals through as the duration allows you.
It’s nice that you want to do damage as a healer, although believe me when I say this, Earth Elemental does absolutely no damage at all, so the mana you spend on casting it is essentially wasted. You should instead be casting your Fire Elemental it will do a lot more and precasting it will make it close to ‘free’.
You should consider running with Ancestral Swiftness instead of Echo unless you desperately need to additional charge of SLT. The added haste will make the spec have a slightly better flow and the instant cast can be used either to snipe or to plan ahead (essentially the same).
Now that you have chosen to be a Draenei you should use Gift of the Naaru, it should not be underestimated. It can make up ~0.5-1% of your total healing, so you might as well use it.