If we're talking about healer performance, I see no reason to choose WHM over any of the other healers, let alone SGE. The Misery buff really helped WHM catch up with the healing capabilities and DPS uptime as the other healers, but WHM still lags behind every other healer in overall lack of damage, limited mitigation tools, and utter lack of utility.

AST, SGE, and SCH all feel more balanced with nuance, and any combination of these 3 has its own merits.

SGE also lacks utility like WHM does, but actually does have numbers to back that up. Play it well, and SGE is able to edge out SCH and AST in damage by a fair chunk. It also offers the most consistent sustained healing, largely invalidating the need to worry about chip damage on the main tank, and has lots of mitigation to keep up with hard hitting raid-wides.

SCH shares some of SGE's strengths in mitigation and sustain, though offers lower total damage. Chain Stratagem helps to a point, but a good SGE will still outperform SCH. Instead, SCH offers some elements of utility that can help parties that may continue to have difficulty with specific mechanics. Expedient helps for position-heavy mechanics, and deployment critlo is the largest party barrier in the game, enabling a team to survive through really busy mechanics or messy performance. Neither of these are necessary, but they add a layer of safety that SGE does not provide.

AST offers both incredibly burst healing and sustain healing. SCH and SGE is a powerful combo, but can at times struggle with burst healing where AST can resolve it entirely with Macrocosmos by themselves. Their biggest weakness is their low total damage contributions, but since a part of that stems from party buffs, even moreso than SCH. For statics, healers are typically lowest priority on raid gear, but AST's buffs will be further enhanced when their party's DPS get new gear, making them that much more valuable in the early stages of a raid tier. This is true for SCH as well and hurts WHM and SGE.