S-tier Units in Your Mind?

Everything that you listed is pretty much S-tier to me, I can't go anywhere without seeing Brave Lyn on an arena team. I'd personally consider regular Ike, Lucina, Brave Lucina, Effie, and possibly Azura/Ninian to be S-tier as well.

Regular Lyn (mine runs L&D and Escape Route with Galeforce and +atk/-res, she is amazing)

Nino (even without buffs she is still the best green mage in the game)

Lillina (Raven Adept Lillina can't even die to Bridal Cordelia or Brave Lyn quad builds and 1 shots both and Swordbreaker lets her slaughter low res sword lords)

Sanaki (same as above, but lower defense and more excess res)

Fae (hardcore anti meta unit that can be built to fuck up greens and blues and can even handle a fully buffed Quickened Pulse/Moonbow Reinhardt on bait)

Zephiel (only if given Distant Counter and Bonfire; he's a red Hector that has more survivability vs anything but Reinhardt thanks to Wary Fighter and a bonfire trigger is 19 damage so he could even kill blues with a well timed attack)

My list would be the same as yours, plus Julia (the best Reinhardt counter and imo the second best mage) and Azura (the best dancer).

I think Summer Corrin needs to be added, with buffs she reks. Also regular Ike. Dancers could all be on there, Effie, Amelia and Lucina are also worth consideration.

I think Summer Corrin needs to be added, with buffs she reks. Also regular Ike. Dancers could all be on there, Effie, Amelia and Lucina are also worth consideration.

It depends on which part of the arena. For offensive Effie and Nino do really well, the whole list outside of Brave Lyn that you listed would count defensively in my book, though I've not drawn any of them to know how well they play offensively.
Most of the cavalry emblem I run (camus, xander, brave lyn, and cecilia) feel really good, but that IS because they are part of cavalry emblem. Xander as a tank and camus who I've put vantage on have served me well outside of cavalry emblem though.
Adult tiki also does pretty well in my experience, though I'm not quite sure she makes the S cut, I certainly think it seems like she gets ignored in favor of her younger alternate.

Add Nino you scrubs.