All this theorycrafting hulabaloo, your'e missing one big point about Cassandra, it's their skills that are pretty much OP. They can rape whatever tank teams you have at your disposal. They have very fast CD. The samurai can drop your mystic's magic and make them futile. They pretty much have it covered against whatever team they are facing. You give me one lineup that can counter 4 Cass and maybe 1 zoey MW support.
Cassandra Magebane has 4 CD skill, meaning even if you go first or second- Raegar Magebane got it covered, Taegan MW got it covered.
Kiera RM, Dragoon Rhea, Taegan MW, Magebane Cassandra, Merlin Warlock.
Any trigger teams with Resilience can rape them.
Any variation of tank + mystic teams with Taegan MW and/or Raegar Magebane included.
There's your first mistake. No amount of resilience can help you against 4x Cass. It will have 4x resilience debuff at spawm.
When you employ Taegen and/or Rheagar in your squad, you will be facing a dilemma which Cass to target. Each one of them are equally deadly. MB has magic debuff with moderate damage, Samurai will have insane amount of damage against non-tank teams, probably party wipe with his omnislash against non-tank teams, ninja can jump within your backline before 1st round ends, and probably wipe your entire team with one swing on 2nd round, and assassin skill is deadly whatever way you look at it and also very hard to kill.
But the real issue I am trying to stress here, please check my post above.
You clearly haven't been reading my post then, that is your first mistake.
My point about employing a Resilience or double Resilience is that you gain 100% damage output or 200% damage output relative to what you would've without resilience when you're dealing with 4x Cass.
If you go second, you can stop Ninja from jumping first, then stop Samurai from casting. If you go first, you can stop Samurai from one-shotting your entire team, I don't see what is the problem here. Not only that, you are able to jump Rhea Dragoon with a Miracle Rune in to stop their nonsense, Cass Assassin with Rhea Glad is equally potent in countering or as a general usage in Arena- My point is, there are plenty of counters, you just haven't really found them yet, I don't see why you should make such blanket statement about '4X Cassandra breaking the game' when it is clearly not true, you have no proof, and it's all straight up theorycrafting.
Just for your information, this is an archer team with NO resilience rune yet, with resilience rune, their output would be doubled, and it would be trivially easy to deal with 4x Cass. As an AI, I don't need to say but I'm sure you know that archer AIs are the least forgiving in terms of algorithm.