I like some revenge stories. Particularly when the MC is meticulous and takes revenge on each individual in a way that fits them uniquely.
This time, the "revenger" wants revenge, but he has no plan and he just looks petty.
I don't really mind the misunderstandings, they are common in this kind of stories. Though I always have a moment of frustration with stories that could be solved with everyone taking 5 minutes to talk things out, I let it pass.
But I can't stand cheap losers as important characters. The exiled one here might have become super-strong, but his personality is still cheap and weak. Worse than the vast collection of MCs with inferiority complex we can find anywhere.
At this point, best thing would have been for Est to die in the dungeon.
Best outcome of the story would be for Est to become the demon lord, she becomes strong, kills him and realizes that everything was her and Daru's fault.
Two interesting options.
The first one was out by design. The idea was to reverse the usual story trope of the MC being banished and becoming super-strong. So this part had to stay, but the viewpoint changed... Kind of. They did turn Est into a petty loser, which most MC aren't in the "normal" setting.
The second one is unlikely. It takes a good writer to implement proper character development like the one you proposed. More likely, the manga would go along the lines of "exiled becomes demon lord, party leader kills him and realizes that she did well dropping this loser." Because who cares about childhood friends and moral dilemmas?