Daily roulettes refers to the Duty Roulette option in the Duty Finder. Every day you can queue for any and all of them (that are unlocked*). For sub-50 characters, that's likely only Duty Roulette: Leveling, Guildhests, and Frontline (PVP). Leveling gives a lot of xp so it should carry you to 50 fairly quickly. Then, you can start work on unlocking Alliance Raid Roulette (which gives more xp than Leveling roulette) after finishing the MSQ, and so on.
Yeah, it just sucks that by the time you're basically able to fly in a zone, you really don't have a reason to go back to it(unless you're a crafter). Especially without needing to level up multiple "characters" along the same zone routes.
To an extent, the full ShB stuff won't be done by 5.3, since there's still the 5.4 raid content which obviously is heavily tied to that. Also while they're saying it'll be finished, it doesn't mean everything there is done just like previous expansions. If you look at SB for example, in 4.3 you liberate Doma fully, but you spend most of 4.4 and 4.5 still running around to discuss thing with weeb Cyan and worst girl while the Empire is doing what the Empire does. It set up ShB stuff with the Scions but a large part was still part of the main SB storyline even after the "end" of the arc. I fully expect it'll be similar, 5.3 will see everyone sent back, but you'll still be able to cross over and you'll probably have some reasons to do so.
