I use a pretty similar team to yours. On magic, I use Kimi instead of Stag Knight, and I use Helicath instead of Valk. For damage, I have Geomancer, who replaces Duchess on your team. 

To make it easier, you really want a champ that can do decrease speed often. Especially with someone like Valkyrie who does group buffs, that could fully fill IT's turn meter. I'd get someon with a Decrease Speed on their A1, that way when they counterattack they have a chance to reapply it after he cleanses

I run Geo, Kyoku, Godseeker, mausoleum mage, Lord Champfort in every and all affinities.. matching affinities is a lie!! Haha I use Lord Champfort as the lead for the super extra hp boost because defense means nothing to IT.. and his passive lands decrease speed so that's taken care of and not ever a thought process.. mage constantly cleanses.. keep Geo in that second slot so he is the first to revive behind  the lead of course if it comes to that.. 

If you don't have lord champfort then tomb lord works great for his A1 to decrease speed. You want a cleanser, healer, reviver, block damage/ally protect while keeping decrease speed up all the time then geo will take care of the rest.

At the moment i use

Gnut-Gnut-Yumeko-Mithrala-Alaz on all affinities but magic. Its a really quick run.

On Magic i use

Gnut-Geo-Godseeker-Mithrala-Yumeko

I think Geo teams are pretty much the way to go.

I use mirthala I have irish orger lol the name escapes me I use geo godseeker and warlord and I have been able to just yesterday beat all the lvls on the different anfinitys

Shamrock.

Update: For Magic Affinity I can farm the boss using this team. All affinities done now.. Fully Booked Geo was key

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