People are hating on dailies, but WoD had no dailies and people talked about how bored they were.
That's because, in a WoW-type game, you need a clear objective that progresses something (your craft skill bar, your ilvl, your level, your faction, your gold pile, whatever).
I think that what people hated in early WoD isn't the lack of dailies. There were dailies, they were just disguised as daily respawns and cooldowns. Each and every work order is a disguised daily. The once-a-day mine and garden. The profession cooldowns. What people hated was that each and every of those happened in their private instance, with absolutely no world interaction, save for the one official daily (well two if you counted the pet battle, but this one was also within the garrison) and the daily heroic.
Legion is trying to shove everything back in the world without having you tied to the "head back to quest hub to turn in" syndrome that everyone hates. They could have constantly respawning missions, but those would cause two problems: if you want the objective to be achievable by casuals, but not be over by the hardcore within days, you need a quota system for the latter. And two, if you have enough objectives spawned that you think you can do "today", then you're going to do all of them, to the point of burnout. They've seen it with the pandaria dailies: they tried "no limits", and people would burn out themselves trying to do every single daily available.
(yes, people are incapable of disciplining themselves. Spoken as a former alcoholic, I know it's horribly hard to, and for most, the will isn't going to be there)
what is your idea for content that even the most casual players can stay busy with?
Content that you can find. The big problem, and it has been raised multiple times, over almost two decades now of MMORPGs, is that people can't be arsed to find their own objectives. A lot of them need the game to tell them what comes next. If there's nothing showing, they're a bit lost. Dailies offer a good way to put those objectives in front of the people.
The main problem of dailies is that they're not new. We've had dailies for almost a decade now, so we wish for some magical better form of daily content. That's why they're moving dailies from blue "!" quest hub to map; they're trying a new form of delivery for "today's content I might do".
TL;DR Dailies are a compromise. Not optimal, but better in general than most alternatives.
