Its weird that he is acting like they put him through so much when all they directly did was revive him, berate him for being a healer and teleport him away.
Yea, they are horrible but There's not really a reason to be a edgelord
Aye. This revenge business would be far better if he had actually suffered greatly. If they had first teleported him into a prison cell, mistreated him, like made him clean the remains of the myriad people sacrificed for the hero summoning, while insulting, kicking, and whipping him for being too slow. After that, they would have sent him to the dungeon. In the dungeon he would have been suffering for weeks at the mercy of strong monsters, almost dying multiple times and only surviving due to his healing spell. He would have needed to eat raw rat meat and whatnot, falling ill in the process. Only then he would have finally found the potion, already at his wits' end and beyond desparete, with no strength to spare anymore.
But nah, he walked for a couple of hours, by the looks of it, got minorly wounded by the mimic, drank the potion. After that he has never been in any danger or struggled. So, his biggest grudge against the princess and her country is because they looked down on him and attempted to kill him, yet not being anywhere near succeeding. It's so hollow and almost corny he's now torturing them and destroying the whole royal court when, in fact, he didn't suffer all that much.