I am unable to set a difficulty level in my games and it feels like it's defaulted on hard mode. In settings you can choose easy yes or no but that doesn't change anything. The AI don't really help out at all, I've had my AI run into a room after telling them to stay and they get annihilated in 1-3 hits. Why do heavy hitting enemies spawn on the first floor? The AI doesn't manage the turrets or anything like in DotE, it feels like you're being punished for playing solo as there is very little to no management that you have control of and easier modes don't exist. Why is it that the only way to heal now is through health packs? Why don't they heal automatically at the end of a wave like in DotE? I'm forced to research food only because if I don't I can't buy med packs that I'm instantly having to use just to need more after the next round because they don't heal. When I have seen the characters heal at the end of a wave it's not to full and if they've been downed or their health is in the red they will never heal. There is no pause option so you can go to individual characters and try to heal them (if/when you do have a spare health pack) durring fights so you watch them die or try to switch to them to help just to get hit by an enemy that does halth their health a downs them. Enemies spawn so much and just ignore the turrets to the point it seems like the turrets don't exist. I try to research more turrets but the monsters go straight for it and I can't send any one to defend the research as the waves of enemies are pushing into the crystal room so I loose my resources and what I was researching. The first floor does not let you prepare for later foors, by the time you get out you have no health, no health packs, have lost all your loot, and possibly researched 1 new turret. It feels horrible to play when you find good things to put on a character just to instantly loose it in the next wave because they can't heal, you have 7 food, and no health packs on the first floor. In DotE the first floors feel more balanced in letting you gather resources, the turrets feel like they do more, and there are even healing turrets. I have not run into one healing turret option. I feel like healing after a wave and having health packs for mid-fight healing is balanced, especially for easy/normal runs and the no healing, no healing turrets, med pack focused runs should be a hard mode option. In DotE you have more management control while in Endless Dungeon you are forced to play hard mode and are punished for playing solo because none of your friends want to play or like these types of games.

This is very similar to my experience, I personally have not played DotE but going from what you have described it seems like some of the mechanics implemented in this game are a step back? I did wonder why the Ai companions don't manage the Turrets or even pop their Abilities when in a crisis, as it ends up just basically, constantly swapping Hero, when the later waves kick off. I also agree with you healing packs should be more of a Mid battle heal, Completing the wave should return some Health, or Fully. as it does with the Turrets, this should definitely be the case if "Easy Mode" has been selected in the settings.
I am playing on Xbox Series X and with no current Cross-play/Gen, Can't even couch co-op with buddies. other than the options of playing with Randoms, so I am also relying on Ai, that only just manage to hold their own on a simple wave, in this era of gaming to not release with this.. seems bizarre to me.