First off: MC being bullied is normal as a story motivational concept. Standard trope. MC being sent alongside summons of class. That's fine and becoming mainstream. Someone standing up for MC when he's getting bullied-par for the course. Where it falls apart is that the MC is so self-absorbed that he thinks that he has NO RESPONSIBILITY in the matter. He is LITERALLY told that he has to DO something to stop being bullied (real shocker folks). However he somehow tries (and fails) to cast the person telling him that in a negative light as someone with a "sense of justice" BUT THEN turns around and blames everyone else for not doing anything as he is being bullied as he goes off to commit suicide. YOU CANNOT HAVE IT BOTH WAYS. MC is blaming everyone else for not doing anything when he is being bullied and then when someone IS trying to help him by getting MC to DO SOMETHING ABOUT IT he discredits them for trying to help. Accountability? Standing up for oneself? Nah I'll just chuck myself off a building instead, that'll show them all. WTFITS? It's basicaly summed up in these lines:

No child... just, no. The bully may have contributed to the suicide as a driving factor, but suicide is ultimately the selfish act of killing oneself. The bully did not chuck the MC off the side of the building. THAT would be him "effectively killing someone" or in other words: murder. MC is hiding himself behind a victim mentality where everyone else is the problem just so he can abandon responsibility. When the basis for your revenge is your own lack of responsibility, you likewise lack any true credibility for vengeance.

Second: Healer is being classified as a tr*sh profession in the other world because they prioritize firepower above all else.

Bull. Sh*t.

Anyone who understands the basics of war will value the idea of a healer no matter how powerful a weapon they desire. When you look at the casualties of war throughout the recorded centuries more fatalities stemmed from diseases and infections than from actual combat until you hit more modern times with sanitation efforts. Go see how many people are still alive today due to combat medics and battlefield medical staff ranging from surgeons to technicians that would have otherwise died. Go ahead, I'll wait. No matter how asinine rulers might be in this other world, there must be an adviser who would whisper a "sir, we can still use him" to the rulers. Anyone with a lick of sense would see the value of a person who can prevent one of their vaunted heroes from hemorrhaging out on the battlefield. Classifying a healer as useless is like saying "Oh, this person only has the ability to carry a bunch of materials in a sub-space dimension. That's garbage, he can't possibly help our war efforts at all. We'll throw him away rather than have him transport incredible quantities of materials quickly and efficiently to the front-lines to supplement our supply caravans."

The only logical conclusion that can be drawn is that the rulers have a plethora of healers readily available and they realize that the MC (who has literally just confessed himself to have shown a blatant disregard to the value of human life) is better off cut out of their fight. This is a logical and practical decision that is putting the lives of their summoned "heroes" and their own citizens out of harms way by casting off someone who lacks self-preservation and trustworthiness. This further weakens any plot of his vengeance being justifiable. "But teh prinzess laft at me and thru me owt..." So a princess is a spoiled brat who doesn't pull her punches-reality check, kid: in ye olde days citizens were considered property of the crown. Attempted suicide was punished with execution because you attempted to deprive the crown of his property. MC is "lucky" (read: plot armor) he got himself transported elsewhere to try (and unfortunately fail) to sort out his mental issues rather than having a quick date with the headsman's axe or hangman's noose.

like when the MC meets a LV 300 red dragon that the MC help with returning his stolen jewel (was it) the dragon saying he will return the favor but to never see him again or the party or three who manage to corner the MC during the final war but they get rekt by him and you don't know much about them you don't even get some back story nor enough information to actually feel their weight in the world of the story

I read 351 chapters of this novel just for the MC Thanos snapped himself out of existing to rest the world, he did give a better life to all the 4 girls in his party member and he did change the world to a better place by the 4 nudges he did to their lives and made it closer to his ideal world, but the Mc that got summoned after the reset and the MC that I read from the beginning to end before the rest are not the same even after the Mc see the memories about the life he had before the rest he can't feel any relation to the MC before the rest

He slowly tortures the king and princess to death using acid and the grudges of the people they killed and then obliterates their castle out of spite towards the kingdom.

abyss magic

The protagonist, at least in most cases, values exploring the world a lot, because of this the protag kinda puts off investigating because he wants to have the fantasy adventure he always dreamed about.

Even the "most consistent" character, the generic loli beastgirl, doesn't have a consistent traits, as she starts out being a physical damage dealer and instantly switches to being a magician for no apparent reason.