Just finished an Arena Assault getting 4834 points the hard way.
I started out with my strongest team so I could have advanced fights at 716-724 points per battle which is nuts when I don't have seven level 50 teams since all the opponents are level 50 on average.
First off, I managed to win all seven matches. I only screwed up in two matches because one match I lost one unit and another where I lost two units because I had to fight Hector:
In my final match, I had a tough combination to fight because I barely had enough units to properly counter level 50 units.
I was fighting Nino, Brave Ike, Summer Corrin and Brave Lyn.
It was so difficult to counter that I picked Minerva, Tharja, Olivia and Ninian. (I really need Azura for more dancers.)
It's the mountain map with defensive tiles in the middle. After positioning my units, I waited for the enemy to close in. Brave Lyn was the closest so I took her out with Minerva in one hit which is important because she wasn't fast enough.
I had to think for a while with what to do next because Summer Corrin and Nino were in range to attack me.
Used Olivia to dance Minerva, Minerva takes out Summer Corrin in one hit with Moonbow which is important because Summer Corrin was fast.
Tharja strikes Nino and Tharja has 2 HP left, Ninian uses dance on Tharja, Tharja takes out Nino.
I've taken out three units in one turn with no items and Brave Ike is luckily only in range of Minerva.
Minerva tanks the hit and Tharja kills Brave Ike in one hit with Vengeance.
That was the hardest fight because it was the one where I was most likely to lose.
___________________
Edit:
So what I learned to get around beating level 50 units was that I needed units with Brave weapons or that could attack with Desperation.
There's weapon breakers as well but the difficult part is if an opponent is using one or if your unit might not be able to tank the hit.
So I'm going to look at which units to improve next that have Brave weapons.