I can vouch for an cavalry team working successfully on offense. Team is currently made up of Cecilia, Gunter, Sully, and Eliwood, all 4*. (playing f2p, so feathers are comin' in slow....)
Experimented with Jagen and he's ok. Gunter does a better job of being an aurabot since +6 atk/spd almost guarantees no x2 attacks against the team, and his high def helps offset Ceci and Eli being physically squishy. Eli also gives +4 def/res, and that's been enough to prevent any OHKOs vs. neutral or adv. combat. I also wouldn't recommend both aurabots, since you definitely need that triangle adv with firepower to set up an EZ 1-2 turn sweep once enemies move into/just outside their threat range. Sorry Jagen. :(
Another cool combo with this comp is being able to rush a mage/archer on the enemy front line with Ceci and using Sully to pull her back out of the other enemies' threat range (provided they aren't also using horseys).
Based on current arena exp, +6 atk/spd Ceci easily deals with Takumi, M.Robin, and most tanks. +6 atk/spd Sully beats pretty much all swordies in one combat round, which is great since this team has two greens. Eliwood covers Camilla/Hector (this one is iffy, so the enemies need to initiate combat for safety). Basically, I haven't run into any problematic enemy team comps so far.
Only (minor) problems in arena have been from maps hindering horsey movement (tree maps), but that really just forces me to play carefully and kite more to prevent an early Ceci or Gunter KO.
I can't say much on the team's defense, except that there's a handful of successful defenses (230~250) each arena season, so something's working. (Or a just lot of fatal mis-clicks)
Haven't pulled Cain, Abel, Elise/Clarine from the RNG gods yet, so more experimentation is coming down the pipeline.
