Brave Frontier did a bunch of these kind of collaborations. You just kind of have to accept it, as dumb as they are. In Brave Frontier at least, the collab units were rarely top tier (with a few exceptions), and mostly they were just fan service and publicity. The thing that annoys me most about the whole thing is that it's going to push back all of the actual content by 1-2 weeks while they do this dumb banner / event.
So todays daily quests included clear the aquapolis (not available yet), so you have to "waste" 3 orbs on colloseum to do the daily. It's still worth it, because with the January promotion, we get 100 lapis per daily, so if you're worried about wasting arena orbs, do your daily, and spend that 100 lapis on a refresh and net +2 orbs you wouldn't have otherwise (or just eat the loss of 3 orbs and pocket 100 lapis).
Tommorow's the Dark Fina boss event, and she's 100% immune to darkness damage. Be sure to remove your Deathbringer, Demon Scythe, and Moonblade's from your friend unit (if you want to optimize them for the event at least). Diabolos is the esper of choice for the event, because of Man-Eater, and darkness resistance.