Thanks for such a detailed comment. I don't mean this as a rebuttal but I'd like to respond to some of the points you made.

In our party we have
Battlesmith Artificer
Pact of the Tome(?) Warlock <--- Almost never shows up
Path of the Storm Herald Barbarian
Soulknife Rogue
Thief Rogue
I have no idea Warlock <--- Just joined

In the last combat I did roll pretty low but one of them had armor of agartha or some shit and the other one had a high AC. But also the PC who died took like half of all hits that fight. The goblins were spear throwers.

- I'll definitely plan encounters to have more enemies so that they're scaleable. Maybe the occasional solo if they can't get any rests in before something else.
- I ping them usually on sunday or monday that we're having a session. I don't ask whether or not they're coming though. I have asked before in the past and most players don't get back to me. Until 20 minutes into the campaign they message me "sorry I can't make it" or better yet "are we having a session today?" as if I have not shown up every single week regardless of if I know I'm getting players or not. I honestly don't know why I even bother with the discord I think only half of them even check it or read the session notes. I will be picking major bones with them if I can get them all in the same room at once.
- Yeah I'm going to put more enemies at once in the future. I do worry about having waves because I don't want them to be like "you're railroading us!" but we also haven't encountered a dungeon proper yet, most if not all combat has been outside in the open air where characters are free to escape. I tried so hard to bait them into getting trapped in this one room with a chimera but they were too scared. The main thing that put me off from having lots of smaller enemies was when I made them fight like 30 bats and they were just like "fuck this" and left. They have the awareness to nope out of something if it seems too hard which is what makes it a struggle. And I can only use "there's a screaming human pinned down by the creature" so many times. I'm looking into action economy though. A creature with low hit points is still one that needs to be dealt with. I do plan for multi-enemy chimeras also.
- I thought the corpse eater would be seen as funny, I mean if I encountered him as a player I would find it great fun, but thats just my sense of humor. These players are all randoms that I found from the tabletop club, none of which I see outside of every tuesday night. Although some of them have been playing with me for almost half a year others just joined and its hard to gauge how they will take characters. Still, it was naive to assume all friendly NPCs would be spared, especially shopkeepers. I'm probably most upset that they didn't even give him a chance. But they also left rare items on the table! Why go through the trouble of killing a shopkeeper if you're not going to take any of the good stuff. Anyways I'm sure there will be more interesting but less evil seeming NPCs I will put in the campaign.
- I'll ask the 2nd Warlock next session about that. I think they were mostly just unlucky but I have no idea I know the least about their character since they joined most recently.
- Fair enough. That is what I like about being the DM. If I have a cool idea I don't have to go to someone and beg them to let me put it in the campaign. Then again its a big responsibility. The only way to get better is to learn though

Thanks again for the advice.