I assume you are talking about the double & triple Valkyrie waves in Nightmare Campaign.

I feel like you might be doomed.

You need a way to control them Valkyries so they don't get out of hand.

It seems to me like your only Crowd Control is Elder Skarg + Drexstar, but they are wrong Affinity.

Maybe, you should take a break on Nightmare Campaign.

Come back when you get more hero's.

Sadly my  thoughts  too