Anyone else having trouble scoring arena defense wins?

Equip unexpected skills, like Drag Back, Lunge, Wings of Mercy, Pass, etc.

Other than that, only thing I can tell you is to use the "Level 40 unit + Level 1 unit" to get cheap Arena wins.

Karzytre is right in the sense that throwing unexpected skills at the opponent will catch unaware players off-guard. This is because you only have to net one kill against an enemy for them to surrender since, typically, they are gunning for a perfect run. Were they to go through the trouble of crushing you after one of their units fell, they would end up using an extra Dueling Sword after being forced to enter and then subsequently surrender.

However, that doesn't mean you can give your Armor Emblem team skills like those and expect to sweep the competition. Even if they have Armor March, you're likely to just get outmaneuvered, considering how stupid the AI is.

Although, that doesn't mean that throwing units like Brave Lyn and Reinhardt into your Arena Defense team just because they have amazing movement will work. People are expecting that. Nearly every arena team has a Lynhardt counter.

The key is balance. I find self-sustaining units to be pretty good. Units that have high defense and resistance are good like Sheena or Zelgius. This doesn't mean go Armor Emblem, though, as I explained above. Units that can't be baited are actually very strong (Firesweep users and of course Razzle Dazzle users). Dancers are also amazing, because they throw more unpredictability into the match.

I would say that the ideal Arena Defense team combines heavy balance (all three colors) will movement assist skills like Reposition and B-slot skills like Drag Back and Lunge.

One build I found to be particularly good at landing Arena Defense wins is Firesweep Bow Brave Lyn. People don't have a counter for it. Usually, they expect to throw out their Dragon and just bait Lyn out, but her set forgoes Sacae's Blessing in order to get the jump on typical Lyn counters. You have to get creative with your Arena Defense team.

Finally, to close this comment, I would also propose the idea of building a few units to counter specific archetypes, like, say, Michiah (Horse and Armor), Kagero (Infantry), Alm (Dragons), and Brave Lyn (Flyers). This strategy hopes to land at least one kill against the opponent via effective damage. Haven't tried this strat out yet though so I can't attest to its potency.

I got frustrated with not netting any wins that I made a cancer team of bonus unit B!Lyn, Reinhardt, Olwen. I started netting some wins after that.

My best advice is to run a Wings of Mercy Mage with high Atk that can get Infantry Pulse (or Ostia's Pulse if you happen to have L!Hector) support, with a bunch of units that you know can survive at least one round of combat. I tested this with my team of Lilina, Fae, Effie, and L!Hector, and I ended up getting a bunch of Defense wins this week. (I have Draconic Aura + Wings of Mercy + Quickened Pusle equipped on Lilina, Infantry Pulse on Fae, and Ostia's Pulse on Hector. No DC on Effie, but she carries her native Wary Fighter.)

The idea is to have the Special ready when you Mage engages in combat, either chunking chunking for huge damage or outright killing the enemy. (This build also bypasses Guard, which more people are running to stop Bold Fighter / Steady Breath shenanigans.) I recommend any of the AOE Specials, as they calculate the damage before combat starts and disregards any Weapon Triangle disadvantages your unit might have, but something like Draconic Aura, Iceberg, Glacies, etc. can work, depending on how many Infantry Pulse users you have. (Also remember to put Quickened Pulse on your Mage to get the 1-turn AOE Special.)

Last week was the first in a while I got any and ended up getting 3 running Camilla Emblem, so proud of my ladies. I know the pain of getting nothing and even running Reinhardt and Brave Lyn with 2 WoM dancers never worked

I would suggest using units that are better at player phase, because the AI is just better with them.

I have L!Ephraim, B!Lyn and NY!Azura.
Ephraim: Deathblow, Desperation
Lyn: Swift Sparrow, Poison Strike, Savage Blow x2
Azura: Fury, WoM, Guidance