Like...Ok, damn, in the main novel this hit hard too, even through the normal well we expect a stomp power fantasy kinda dealie. Like it's not a nothing thing that happened, because of Rimuru's orders people died where they could have protected themselves against an actively hostile force. They were certainly strong enough for it at the time I think. But it still hurt.
But man, looking at it from the point of view of folks on the ground ABSOLUTELY hit's different. We get that Rimuru's great, we see how they love him, and...they fail. People die, which hurts worse cause in these three's case, they're supposed to be protecting them or were trying at least, and not only did they fail, they failed while breaking the orders of the person they admire and respect.
Shit, you broke the rules to try and do the right thing and you STILL failed? That's bitter as shit. And it hits harder because up til now this has been a very chill manga so honestly credit where it's due.