It’s not. Your HPS in pretty much every case, doesn’t matter. It certainly does not matter when deciding which item to upgrade.
And the answer to that has been given in the first two posts: you don’t.
Nope. Because you can’t reasonably sim neither a raid nor a key. When your precious sim ends up with 10k hps, while in a +17, most people average around 3-5k HPS, and don’t even peak anywhere near 10k hps, not even on Pride, that pretty much confirms that the sim is irrelevant.
When the sim ends up simming spells that you never use in your spec, leading to a stat weight distribution that is actively detrimental to your performance, simming is not only useless, but harmful.
Because DPS is important. Even for a healer. Go sim for DPS, that is useful. Simming for HPS is not. There’s not a single encounter in the game where you want to gear for HPS. Not one.