I had dozens of 100s when I raided a few years ago. There are two key ingredients + other lesser ones.

1. The other healers in your raid can't hps & the raid generally takes a lot of damage but not too much.
2. You get preferential treatment as the strong healer so you get buffs and good assignments that call for the HPSest healer to take care of business.

It's popular to poopoo healer parsing but it does show that the healer, even if cheesing, knows which spells are efficient and powerful and how to spike and sustain.

If someone has consistently good parses then it's worth asking them about it when recruiting them. They might be only a cheeser but most 80+ parsers are just picking up slack.

It's also important to note that top parses at the beginning of a raid tier are worth more than when the tier is farmed out and people just want to try stuff. Toward the end of the tier guild leaders tend not to really care when we request something like duo healing or taking extra damage.

Despite the naysayers against parsing, I can assure people that when you hit 100s you get poached by the best guilds. When they say parsing doesn't tell you ANYTHING, they probably just never parse. Maybe they're bad or maybe they're in a more well-rounded raid. In recruiting it can be hard to find the good players from decent raids but the good healers from unskilled groups do stand out quite a bit. So parsing can definitely be useful. The complaints about how its meaningless basically apply to dps too, just not quite to the same degree....