MC only gave the last blow, so he basically robbed others of the kill. Also, his buffs and support was weak, that's why they failed, not because of their own shortcomings - it's obvious because MC is a support and weaker than all others. So basically he pulled some stunt or set up this sequence of events to try and benefit off others. Even if he gets paid below market rate, that's still all his fault and he can't be trusted. That's the reasonable explanation for them.
Humans are not rational animals. Some are abusive because of the joy the others' suffering brings them, some get very angry and even hurt when people they see as beneath them seemingly outperform them. There's all sorts of weird quirks that are detrimental but ingrained in behavior/thought.
No, I would agree with cgr here. If you are incapacitated by monster that had little visible damage, and you wake up ALIVE, because the last man standing was able to kill it, the position of being in a life-or-death situation is "oh my god I'm alive", and gratitude. This is a repeatedly shown in the real world with natural disasters and war. The first thoughts by the other party members would not be "oh, he stole our kill", but "we were THIS close to becoming a carnivore's snack, thank god the last guy did something that kept us alive" - especially after seeing the state of said monster before and after being knocked out. None of this is based on "rational thought", but repeated observations of most animals in times of crisis. We have seen tame and wild felines, canines, birds, equus and apes exhibit what would be deemed "friendly" behavior to their rescuer after rescue from grave injury or situations where the animal is in a state of a
life-threatening crisis. Humans are no exception.
In reality, what you are looking at is a cheap story hook that is at play. The writer is following the template - make a quick script that gets the protagonist alone and onto the "hero's journey" but skip the whole part about the growth of character strength. The method to start the story in this case is "I was kicked out by people who think I'm worthless!"
It makes a short series and doesn't require much thought, or a series that copies a lot of scenarios that take little to no effort for the main character to resolve (i.e. appealing the hero's triumph gratification). But, it pays the bills, and you can spend more time on the artwork than on the plot.
So what differentiates good from bad writing in this format?
I can't answer that question for you. But I can answer it for myself:
The main character's struggle with themself. The incremental changes of their own personality. The method they realize their own worth. How and who they transform into for the better, or - if you want to go the tragedy route - for the worse.
