It's called being prepared and I'm saying it's nothing unique to DLC 3. Butcher wants you to have resurrectionist ring equipped. god's fish wants you to have 100% evasion without using dodge, how you achieve that is up to you. Neither of these put a stop to the tried and true buff stack and one shot though. Nurse call at least forces you to spend turns on buffing. Florence has two phases, the second of which stops you from relying on healing, including no turn cost flasks. If you didn't stat wall her, you also need to figure out how you're going to recover in the first phase as well if you decide to cheese the second phase. It just sounds like you're mad that after an entire game and 2 dlcs, you now have to play slightly differently when the dev assumes you have everything at your disposal and is free to design bosses around that assumption.
There are still loads of useful items from the main game that aren't replaced in DLC 3. Jabberwock's scythe ( and not just for florence), knight's sword, gungnir, hans, bunker blade, elemental resistance shields and rings, resurrectionist ring, black rabbit ring and many more. One fight is the definition of using old items to win or die. Apparently though, you just automatically assumed the new stuff was unequivocally better because the number on the DLC was higher. If you want to make the claim that the new items are required for the DLC 3 fights, you should give an actual example instead of being vague. I am 100% certain though that I could beat the DLC without using any of the items it introduces.
The fact that you bring up storm ruler of all things shows your inexperience with the game. Storm ruler's special attack isn't even that strong compared to something like blood edge or hans (which is found in the same place but no one mentions how godly it is), neither of which get a replacement in DLC 3. Everyone uses it though because it's easy to get and makes grinding easy. Grinding so they can easily stat wall any boss.
Whittled ring isn't even useful. All the % hp damage attacks bar one do less than 100% damage total before you get a chance to recover. You're talking out of your ass. If you died to a % hp attack (while having 100% health), it's because it also did regular damage which, shocker, you could guard against. That one attack I mentioned? It's a breakable attack so even in that case whittled ring is useless.
Being a player longer (whether you are or I am) has nothing to do with being able to appreciate the gameplay. I'm not saying the game is faultless either. Most items not taking turns is terrible with how useful items are and makes me wonder why some status effects like silence even exist. Status affliction and break being reliant on literal luck is terrible. The damage values on magic skills are almost across the board half or worse than just chaining the strongest physical attacks. Unis is a terrible fight because even with 4 +3 sniper rings and gungnir, you can still miss.