Supposedly dlc 3 content will be very difficult. One of the bosses at least is recommended to have 10k+ stats. That's on difficulty 0. From difficulty 0 to difficulty 9, Miranda goes from 658400 hp to 4602300 hp, almost exactly 7x increase. Those numbers might not be exact since I was using jabberwock scythe to check. Also, consider that with 10k attack, you can get 45k attack with double attack buff (1.5x), phalanx(1.5x), and madness(2x). However, if you already have 110k attack you can't buff it any further. If the boss is balanced around using just attack buffs and not phalanx and madness, that bumps the stat check to 15k. 7x those stats from difficulty scaling would be 90k. Remember, you are at 110k stat and can't increase that at all. So if it's balanced around that, then maybe the boss will be a little weak. If the boss is balanced around using madness, phalanx, and generic buffs however, then it is going to be a very long fight.
Additionally, The God Inhabiting Lake, who I think has the most health of any enemy in the game, has 10,000,000 hp on depth 18. Even with 110k attack and using frumious wrath, the strongest attack in the game, you only do like 40-50% of his hp without critting in one hit (crit him for 15m though). Considering that dlc 3 is intended to be harder than both the chaos dungeon and the sea area, at least the last boss of dlc 3 won't be one shot, probably. One turned is definitely a possibility though. Once frumious wrath is charged, you can use it repeatedly for the turn you have the buff. 4x black rabbit rings + duchess covenant = 6x frumious wraths. Remember to use indignation the turn before and that's 7x. Also make it bleed and swap to butcher axe midway through your turn. Crits are 3x damage. 5m x 7 x 3 x 2 = 210m damage. It's dead. Could get even higher if it happens to have an element it is weak to.