Are you really concluding that SCH's were ACN's to begin with based on "Arcane Mastery"? Is this the depth of your knowledge of SCH lore? If so, these links might help:
What it means to be a Scholar - Uploader Synonic Scribe
Scholar, post 7th Umbral Calamity - Uploader Sync Weaver
War of the Magi, and the 5th Astral Era - Uploader Synonic Scribe
A little Arcanist lore - Uploader Wyrm Limion
A little Summoner lore - Uploader Synonic Scribe
Of course, I don't expect you to look at all of those. They do make for some good viewing if you have about an hour and fresh cup of coffee. I am posting these more as source material to show - a lot of it verbatim from the encyclopedia - that SCH roots really aren't defined by the ACN class, or even really by damage.
What is really important to note is that classes have their own lore. Some classes keep the ties stronger from class to job, but every class, and every job has their own lore. In the case of ACN, SMN, and SCH they all weave spells in a similar fashion, but they are each their own separate schools of arcane arts, or magic. How each of them came about to use a book/codex/grimoire as their arms can be traced to the southern continent, and it is likely from here these practices branched into their respective arts.
The green plague you refer to, if the same as I recall, was foulplay at the hands of the mages of Mhach. It had absolutely nothing to do with how the SCHs of Nym practiced their arcane arts. The SCHs of Nym were mostly pacifists, and desired to stay out of the conflicts between the city states of Amdapor and Mhach. It was the latter's inevitable desire for the conquest of Nym and their resources that really forced their hands and aid of the mages of Amdapor.
The SCHs of Nym were practiced in battle tactics and strategy. Their strength lied not in their own combat prowess, but rather their ability to direct and command their fellow marauders into organized and optimized battle formations in combination of the deployment of their shields and curative magiks to assist and support their allies to easily overwhelm their opposition. This whole Bio+Misama into Bane, then slap on a ShadowFlare... that is ALL Arcanist.
Again I will recommend the links to brush up on your knowledge. The SCH's fairy wasn't always sentient. To this day, no one really knows how this came to be. Because of this, we really don't know exactly what they are capable of. No we haven't seen them cause damage, but I also wasn't being strict that the damage had to come from Lily. Only that she be involved somehow with the animation.
Sure it has. It's the players pining for 3.x SCH that have remained stagnant. The rest of the game, and SCH has moved on. Going on five years now. Holster your savage tier epeen bud. I merely said I was not sure if it would be viable, but just because you say it is, doesn't make it so. I don't need to run savage or ultimate to know that SCH's offensive kit was consolidated into Broil and War. I don't need to run savage to know that if SCHs old kit was just thrusted back into their repertoire, they would need some serious adjustments, to you know, make it viable for content.