That's it entirely. Part of the battle redesign is to reign in the massive AoE in dungeon runs. It's not just SCHs and SMNs that got hit, but Fire II, Flare, and other AoE abilities also got hit with the nerf bat. Some got hit harder than others. Part of the design is to help stop the massive pulls as seen in dungeons.

As far as the lost to sustain, it's rarely been a problem for me as a SCH, but then again, I rarely use SCH in solo situations. The fairy is capable of healing itself, and the SCH could also heal it or resummon it for it to get back full health. One thing I've noticed going over the job guide is that they're encouraging summoning the fairy to build up the gauge.

If anything, I'll feel the loss of Sustain on my SMN, as I use Titan-egi to tank for solo fights, and I used sustain to keep it alive. It means that I'll have to use Physick more to keep it alive.

One thing that I do find a bit perplexing is the nerf to Embrace as well as the increased MP cost for Adloquim. What was the logic there?