Making Afflatus Misery always a DPS neutral action would do a lot of good for both experienced healers and casual healers. As it stands, yes, Misery is always a DPS loss. Even if you're forced to use GCD healing, you are still losing damage, which makes Misery a partial return of DPS rather than a full refund. But WHM is already the healer pressured far more than any other to GCD heal due to an overall lack of OGCD healing that's almost ubiquitously outclassed by tools every other healer has access to. In other words, they lose a lot more DPS uptime due to just not having the resources to pump out free healing like the other healers can.
Having said that, though, I think keeping WHM as a low APM job is a good thing. There are a lot of players that want something slower and easier to play, but that doesn't mean WHM needs to be boring either. It's totally within the design team's power to make WHM all about making impactful choices with the spells they choose while still allowing its tools to be forgiving.
Making Misery completely DPS neutral, without any other changes, would make quite literally everyone happy. Experienced healers would be fully encouraged to take advantage of the GCD healing for once in the history of FFXIV as you benefit from being net positive on HP while maintaining your momentum. Meanwhile, casual players benefit from a naturally raised skill floor since you're promised a certain amount of optimal DPS every 90ish seconds, though you also aren't pressured to pump out as many Miserys as you can. So even if you are optimizing, you can sit on full lilies when no healing is needed and not need to use them.
The only potential concern is encouraging pumping out Miserys during burst windows. But for casual players, that's not something they're thinking about anyway, and we could also resolve that issue very easily by just giving Misery a 20 second recast time, if it even would be a problem at a higher level of play.
What I find ironic is that it aligns perfectly with the design team's goals of healing. It almost feels like they won't do it to spite the midcore/hardcore audience even though it would also benefit the casual audience. But then again, they also heavily nerfed Thin Air. You know, to make healing "easier" and "more accessible."