S Tier is almost always a function of “extra’s” brought to the table in ideal circumstances.
In the case of Healers, this comes in the form of Passive DPS, mitigation and other utilities. HPS is very rarely much of a consideration because in a “perfect group”, provided you can keep the Tank alive and heal (or mitigate) the group damage, no one really cares what your HPS is.
In 99% of groups who don’t play perfectly, and (for example) spawn the Prideful add after face pulling an extra trash pack while their HPally has no CD’s, Paladin is most definitely not “S Tier” because their DPS counts for nothing when the group dies from AoE damage that the RDruid/Rsham easily dealt with.
I’ve been enjoying my Holy Paladin more than I expected I would, but there are certain Affix/Key/Group combo’s that I won’t go near.
I did recently swap from Glimmer to BoV which definitely helps out during those chaotic moments, but it feels like 3x the work to achieve the same outcome as a single Wildgrowth onto a group with rolling Rejuv’s.