You are correct that Deep Archimedea is harder than Netracells. It is currently the hardest thing in the game, and in order to get higher rewards you have to make it even harder with the modifiers. Also, since you mentioned that you don't use Charge on Rhino, you should try using the Helminth to change it out for another ability you have unlocked. Last thing, there are still two systems you have yet to unlock for the Helminth. One is from Bird 3, and the other is from Son/Kermerros.
