It's very funny that people hate MC so much, ffs he is just an ordinary NEET and shut-in playing video games and reading manga. A typical Otaku. He never had any experience in fighting or anything and is summoned to a world full of magic and swordplay. Doesn't matter how much he trains at the end of the day he is just an ordinary guy. It's not like he can pull some random ass powers or go full one punch on his enemies no matter what, it's the reality. Just because you felt a lot of despair doesn't mean you get supernatural powers just like in real life. BUT you can only cry in agony watching people close to you in unimaginable ways and ultimately waiting to just die to reset the timeline.

And after the reset, Subaru goes back to the last saved checkpoint completely dazed. Because he can remember everything from the previous timeline, the horrible deaths and his own. Time is running out and you can't think of anything or make any plans on what to do next because there is so much a guy can take that the trauma from the previous timeline itself is just truly a pure terror and there is no time to grieve or snap out of it, whatever he witnessed was real but its all erased because he is dead. The body remembers it and you don't wanna go through it ever again but it's the harsh truth, you gotta die sometime again if you aren't careful. So as Subaru progresses into the next arc successfully without any major deaths, he can't foresee what's gonna happen and can only plan after making some trial runs through the timeline. Therefore deaths are necessary to successfully plan ahead without major casualties. And that's the harsh position to put someone in, because *nobody wants to die*, however quick or painful that maybe and that's the only thing he can do.

If you still hate him so much, just put yourself in his shoes, what will you do? Yell or train all you want but you can't get any powerful.
You can't do anything but do *EXACTLY* like him.