So the story's main faults that make me want to drop it is the power system, character relationships, and food (Although this one is more caused due to a lot of novels, not really this one)

To start I'll do food since its by far the most minor and pointless of my complaints, but in the story there is a lot of interjections about "korean x" that adds nothing to the story and while its pretty easy to skip over it just feels a bit annoying. Its the same trope of the main character cooks korean food and the other party involved (in this case the demon lord) is shocked by how delicious it is. While this is very minor and something you can easily skip over this novel just happened to be the one where I'm tired of it, since while its not in every korean novel I can think of quite a few off the top of my head where its a korean MC, they make korean food and characters get shocked by how good it is, and food is constantly being added into the story. This is also an issue with a lot of japanese novels that do cooking (death march for example) where there are long descriptions of food, and with most of these they serve no value and feel like they just inflate novel length without adding anything. Overall while I don't mind how its done in some series (off the top of my head the angel next door spoils me rotten) food in stories is I think often has way too much about how its being cooked and other random food things that just simply don't matter in perspective of the story.
It might just be since I don't really care about food, but especially for novels like this one that feel action/adventurer I just find it very tiring to have cooking be basically 50% of the plot (I made food, she punched me to train x, lore, I made food, bit of training, I made food) and I think these scenes are meant to build up the relationship between the demon lord and the hero but instead of actually doing that instead its focusing on just the food and the demon lords reaction to it, which does nothing for their relationship.

To continue my second point about character relationships. The relationships in this novel feel incredibly weak and forced. So to begin we are informed that he has a party, but since it skips to the end of the demon lords fight the sole development there is that he had some kind of bond with the strongest hero, a woman in his party, but she instantly dies so we have pretty much nothing there. To continue with her after she gets regressed, revived, ?, she starts to instantly look for specifically him and not the party. I honestly assume that this is just due to the author having the common problem of everything revolving around the MC, but giving the benefit of the doubt it means that she cares enough about him specifically to search only him out. But again, there is no real relationship between the two that we know about, and while I'm sure it will expand later at least currently the way it was done makes me not care for her as a character, since she barely exists with our MC. There should of at the least been a scene where she dies while he is trying to protect her, have him get upset at her death, have some kind of interaction. If there wasn't the scene of after she got revived there is quite literally THREE sentences about her, and thats with me being incredibly generous. (One is her line about how she can't protect him, the second one is saying she is the strongest hero, the third just has "she fell" in it) so there is quite literally nothing there.
Then the main character himself is a f*cking brick. Supposedly every except for him has died and he has quite literally zero reaction, the next lines are about how he took the wrong path. It wouldn't of even been that hard to add three lines about how he as a tank did a su*cide charge out of frustration or anger, have him get pessimistic and think everyones deaths, including his own imminent one have been pointless, have just some kind of reaction to this slaughter that included everyone he has been with for the last fifteen years. At this time he has no idea they will be revived so why does he treat their deaths like it doesn't matter.
Then once you get past that he still has zero to him, his sole traits are 1. food, 2. strength... thats it. In this book it has shown that he cares more about food than he does about every other person with him being killed. Outside of food there is just that he trains... Granted, you can say I'm early in the story but by this point in the story the character should at least show something.
This novel seems to be setting up that the demon lord is becoming close with him during their training but its so incredibly forced that it feels more like the demon lord is just incredibly desperate. There entire relationship I think is a train wreck from the start, because it begins with her mu*dering literally all of his comrades yet that issue is glossed over like it doesn't matter, because our main character is a brick. While he does overheard the bit of dialogue about them being regressed from his perspective the person who is the main enemy, who just killed all of your comrades so recently that their blood is still warm, and the s*upid fairy who slaughtered someone at the beginning are the ones making these claims. While I understand that the story needs to go on the speed at which he gets over it, or lack of anything related to this, just makes the main character feels so fake. The start of him and the demon lords relationship could of been him holding a grudge, her accepting it and taking responsibility, with him gradually trusting her as she helps him train. Instead its [She kills his comrades] -> [dialogue about regression] -> [we cool now] where it lacks even the bare minimum.
Anyway, I'm getting tired of writing this but there are just so many things where the characters themselves are very bad, and that causes the interactions between them to be basically non-existent.

Ok, part three. Tired of writing this so I'm just going to do it quickly. Things like him suddenly having spirit abilities, things like how he can suddenly get job class & stat growth. Skipping over things like equipment, while still stating equipment (like how he cooks on x shield). Things like his skill resisting regression, how regression steals skills, ect. Things like him quickly growing stats and being surprised (along with demon lord being surprised)

Overall, the novel feels to me like it has very weak character development and it also suffers from the common everything revolves around the protagonist. But still giving 3 because its not bad per se, and a lot of this is probably just fatigue from the genre and this novel happens to be the tipping point.