I don’t know much about Frida, but I’d try
Boldtusk - Frida/Grimm - Kash - Joon - Kunchen
Evelyn - BT - Kunchen - Frida - Joon
Frida | Boldtusk | Kashrek | Kunchen | Joon
^ that team right there will make your center very tough to take out, at the raid level you are. You should have no issues staying on high platinum imo, such that you can get near diamond and open your chest quickly for the better chances at good ascension rewards.
Would you recommend waiting until kunchen is maxed before putting him in the tank position?
Yeah, I would tank with Kashhrek and flank with Kunchen, until Kunchen is maxed at 4/80. Once that happens, you can tank with Kunchen, and bench Kash:
Evelyn | Boldtusk | Kunchen | Frida | Joon
Something like that would work well for e.g., also assuming Evelyn and Frida are maxed by then.
Reasoning:
Kashhrek is more tanky at 4/70 than Kunchen is at 3/70. Even though Kunchen has a natural resistance to def- he still won’t be able to take as many hits as he could if he was maxed. That is important to fire his skill, which is slow. He’s gonna have better chances to fire it in the flank for now.