"The Significance of being here", more like the significance of not making dramatic shift in the difficulty level

I was obviously listing through the Season 3 campaign, just completing the levels to gain SG diamonds, and I've gotten myself into that mission named "The Significance of being here".

Now, everything was fine up till this mission, where I just died 3 times already because the game just throws batshit insane amount of overpowered enemies at you for no reason, and I just ragequit at the end.

I am using braver with hunter as subclass, so I have the auto mate heal items skill maxed out (Even though I hate being so dependent on it, I plan to switch to a different sub-class in the future), so I pretty much regenerate my heatlh at any point but due to how every corridor in that mission becomes Touhou bullet hell, you eat through your healing items very quickly, thus die at the end due to lack of healing items to keep your health up.

What I am saying is, previous missions we're alot easier, and thats with the fact that I played in Hardcore difficulty only. The enemies in previous mission would easily die from one or two slashes of Flash of the Lotus and Crafted Cherry blossom finale easily, plus it didnt spawn them in such insane amount of hordes either, so I would able retreat properly and make counter-attacks.

This is just different in the story quest "The Significance of being here", the corridors are smaller, and the enemies there for some reason have much more health, so I would need like 5 or more Flash of the Lotus slashes on to kill one, the level also spawn an insane amount of them, making it very difficult to dodge all of the swarm of attacks.

If this is the one where you're in the corrupt underground shafts area... this is actually intended. The story from there onward is meant to be for level ~70 or so (and in a party actually.) The mobs were meant to be higher than the level cap. The story content there was also added in Episode 4/post-Ep3, not Episode 3.

I'd recommend not doing the mining base defense mission that comes after it (with the towers / AIS) until you have a Scion class.

(I'm of course talking about Normal (JP)/Hardcore (NA/Global) Difficulty. The strength of enemies is the same on JP for this difficulty.)