Does that really ring true with healers anymore though?
If we compare vs WHM:
SCH's increased difficulty comes down to needing more proactive vs reactive, you need some fight knowledge to shine. However even that isn't really what it used to be. ARR SCH used to have objectively weaker and slower healing throughput than WHM. If you played reactively you could genuinely struggle. Now that's just not the case as the holes in the kit have all been plugged. A well played SCH isn't easier, they are just more efficient with GCD usage (More broils basically). Challenge doesn't really come into it.
AST is much the same, they used to have weaker raw healing throughput and less of an emphasis on personal DPS but with highly variable and erratic cards to make up for it. Now the variance is mostly gone, replaced with fluff variables that barely matter. The challenge now boils down to: Can you do your 2 minute burst rotation whilst also handling the mechanic that's probably happening in the middle of it. That's a fine challenge for Savage, not so much for Extremes and certainly not in anything below where CD alignment is probably a disorganised mess anyway.