• Stop making so many champs lvl 50 (like Warpriest and Heiress), make more lvl 60 champs instead
• you totally underestimate the power of control debuffs like provoke. You have Nari and Umbral, one of them sould be lvl 60 and in your arena team
• you don't have a champ for decrease def in your arena team, Armina could take that part (needs her A2 skill booked to 100% debuff chance)

My suggestion for a team is:

High Khatun (lead for her speed aura), Armina (decrease def on all enemies), Umbral (provokes all enemies for 2 turns, they can't act anymore), Elhain (damage).

High Khatun has to be really fast and goes first, she puts a speed buff on your team and increases their turnmeter, so all other team members can follow up before the enemies get a turn. 209 speed is not really fast! Use 6 items from the speed set. Use boots with speed main stat. Take Lore of Steel mastery (support tree) and only use items with at least one speed substat. Steal from other champs if needed. Spreading your good equip among to many champs is a commen mistake in early game. Concentrate the best equip on a few, often used champs.

Umbral follows with her A3. The whole enemy team can't do anything exept attacking unkillable Umbral for the next two turns.

Armina follows with decrease def on all enemies and 

Elhain comes and finishes them off. If her damage is not high enough to immediately kill them, you have another chance to do so in the next turn, as Umbral's provoke lasts for 2 turns.

i'll second everything skadi said, but i would recommend daithi as your decrease defense champion rather than armina.

your best option for a nuker right now is either ignatius or tallia. ignatius will be of greater use in other areas whereas tallia is more limited and will be replaced by better champions as you progress further though, so i would aim to use him.

I would recommend switching High Khatun as Arena lead with Gorgorab, he has a better Arena speed aura AND increase ATK for your nuker. For now, it's better to keep your current nuker until you get a better one - Ignatius deals serious damage, but you lack any champion with increase DEF. He doesn't benefit at all from increase ATK. When you pull someone with increase DEF, then you should re-asses the situation again.

I didn't recognize this new champion. The number of champs in this game is more than I can remember allready. 😀

I totally agree that this one should be prefered over Armina. Placing an accuracy buff on himself + extra turn is insane. I would like to have this champ in my roster.

This early on, it's good to build versatile champions who will also be useful in other areas. You will use Khatun and Gorgorab in other content, so definitely helpful. 

Like Skadi said, control in speed team is a must. Not only will Umbral protect your other squishy champs, if enemies are busy with her, your debuffer and nuker don't need to be that fast, means you can put more points into accuracy and damage instead of speed. 

Daithi is a beast, so is Umbral. And they will also help you everywhere else.

i was lucky enough to pull him during the x10. only reason i was able to recognized him.

Really appreciate all the suggestions.  Very helpful and informative.

In my defense, War Priest was part of Raid's urging to get 4 5* champs for a mission and was 5* before I had really pulled anybody else decent (or so I thought anyway).  I would think the game would "help" you progress, rather than get in the way.  Lesson learned.  She also was the prime champ keeping Elhain alive until UDK took over that job.  As far as Heiress goes, I got sucked in by the "Clan Boss Goddess" title on the HH website, so that's why I leveled her up ... and worse, used real books on her before I realized I should have just used farmed copies.  <SIGH> 😭  (At least I did NOT make that mistake with Warmaiden.)

For the other 50s, Gravechill was intended for Clan Boss along with Frozen Banshee but very recently was replaced with Kunoichi.  For better or worse?  That's a topic for another time. 😎  But, the comment about too many 50s is well received.

I initially had high hopes of using Armina for Arena but then got dissauded by comments that she wasn't all that and that you really need another Stun champion for her to shine.

Honestly, I hadn't even noticed Daithi ... in fact, I had to click through all my champs 1 by 1 to find him ... as I pulled him in the last 2x along with Ignatuis who's gotten all the attention since then.  Makes me wonder what other champs I recently pulled that are off-screen that might be useful.  For kicks, here's the 2nd page of champs:  

i

Most of these are being levelled for FW until something better comes along or as food eventually.  I need to be better at managing the barracks, but I'm getting side-tracked....

As far as High Khatun, I posted her speed as an honesty check.  I was under no delusions that 209 was actually fast. Just demonstrating how bad off I was. 😗

Last, I had not considered Ignatuis in regards to a Def Up support champ.  Obviously, I'm still very green but I'm trying to learn and so really appreciate the time and effort taken by all to respond.  Time to do some work.

Thanks again.

... AND ... clicking through the new champs that I hadn't yet paid any attention to, I see Captain Temila has a 60% Inc Def buff.  Sweet!

I think perhaps for now, I'll stick with Elhain since she involves no real work and "fix" the other issues and then a little down the road, investigate Temila with Ignatius.

Thansks for pointing out the new champ which triggered me noticing this combo.