To be honest in my opnion i think that WHM it's harder than SCH, it's easier to play casually but harder to maximize it's potential.

SCH in lower level content it's totally braindead cuz your Fairy can deal with everything alone, which allows you to do anything you want.

SCH in higher level does have a huge oGCD and CDs arsenal to use and a high mobility, it's that a hard thing?, Not at all cuz it's nothing close to DPS Role Mechanics where you must know efficiently the best way to fit all your oGCDs under your CDs windows in your Rotation, it's just all about Healing stuff, so it's very intuitive which spell you must prioritize to use cuz every healer works under the same concept.

WHM feels like BLM for Healers, their skill kit isn't that complex at all but to maximize your performance it's not that simple, you don't have the same mobility that the other healers does, you don't have the same amount of oGCDs that the other Healers have, you don't get tons of CDs that the other healers get, you don't have faster Cast times that the other healers have, etc.

In the paper SCH it's a healer where you must antecipate enemies damage preventively, but in reality he's even more reactive Healer than WHMs are cuz you're going to use your oGCD Heals after the damage it's taken 99% of time than your GCD Shields before it happens, otherwise it's a DPS and MP loss.

If you're interested in Sage i suggest to play as WHM, not SCH. The only similarity that Sage and SCH supposedly have about each other are Shields and that's it, everything else seems closer to WHM. For the notes that we got in Live Letter Sage Job Mechanics are just like WHM ones, so probably WHM and Sage are going to be the "Powerhouse Healers" with higher aDPS and Heal Potency, Self Buff to improve their own Spells, Lower Party Utility and GCD Based. While SCH and AST are going to be the "Utility Healers" with higher rDPS and Heal Potency, Party Buffs to improve Allies Performance, High Party Utility and tons of oGCD.