I’m just gonna plug the talent article (https://chainheal.com/legion-talent-builds-en/) and our Cloudburst article (https://chainheal.com/resto-shaman-guide-on-how-to-maximize-cloudburst-totem-cbt/). In case you haven’t read them. I do think they offer more perspective.
Shamans have a passive ability called ‘deep healing’. The lower HP our targets have, the higher our heals heal for. And the relative strength of that is increased by our mastery. This is why this stat is always insanely good during progress, and a bit less during farm (people just won’t drop as low as often).
The mechanic behind crit is called ‘resurgence’. When our (single target) heals crit, a portion of our base mana is refunded. This is why on farm, the focus for resto shamans usually shifts to crit/haste.
With the way the artifact works right now (there are a few traits playing into crit), and the availability of crit. It is actually possible to optimize this playstyle early on. If you are using an expensive spell like chain heal a lot. The crit build allows you more to do so – generally speaking.
The artifact ability is pretty powerful, not using it would be a waste. You don’t have to use it on cooldown exactly. You can look for neat moments to weave it in. But I wouldn’t hang on to it for too long either, 45 seconds is only 1,5 healing stream in cooldown time (which we pop all the time too).
If you read the CBT article, it will become apparent that you can definitely start off with casting CBT on cooldown (paired with HST indeed). As you become more experienced in using this talent, you will start to tweak it slightly here and there. Altering when you start dropping it (to counter mechanics), and when you trigger the burst (to ensure more or some healing). CBT is by no means a must, but it is competitive, intriguing, fun, and with a high sniping/ranking potential.