I also don't see how top healing ranks are relevant unless that specific parse involved dropping a healer compared to the next rank in line. The majority of the high-hps parses come from a player leeching hps from the bad healers, not necessarily running a more optimal composition.
Case in point:
https://www.warcraftlogs.com/reports...2&type=healing
The top resto shaman HPS parse for Mythic Nythendra was accomplished with an extra healer. The other healers were obviously very bad and the extra one was unnecessary. Their raid took 463m dmg, whereas my guild's first kill only took 408m.
Someone getting a high hps parse doesn't mean they are doing something better; in many cases it actually just means their guild is doing something wrong.