This is the problem with Breath of the Wild. Because it's "completely open" people can use any excuse they want to forgive the game. "Oh, you can go there whenever you want!" "Oh, that sidequest is boring? You don't need to do it!" "Oh, you don't like the game very much? Just skip to the end of the game bruh"
The reason why I didn't know that it was one of the toughest bosses? Because the game doesn't tell you what level the bosses are in proportion! You don't go in the shrine and it says "guess what bitch? this is one of the hardest shrines in the game!" What, do you expect me to look up every single thing about the game the moment I come across it? Isn't Breath of the Wild about the wonders of exploring? Do I now have to look up every portion of the game and see if it makes sense compared to my weapon durability levels?
The castle is one of the worst examples you could possibly come up with. It's literally the end of the game, OF COURSE you know from the beginning that it's going to be hard. Combat shrines aren't the same, unless you already know how they scale you can go into one without knowing how hard it is (and before you make fun of me because it said "Major", know that many games use ridiculous and over the top wording for their scaling systems. For all I knew the hardest could have been two levels above that).
Not only that, but I DIDN'T have rusty weapons at the time. This is just a shitty excuse that other people put on me that I never said even happen. What, are you guys going to guess my entire inventory now to make an excuse for a mechanic? Really?
And if you're talking about the treasure that gave you a flame sword ... I actually got that. You might be talking about different treasure though. Guess which boss I broke it to?
The game didn't tell me this or that, whaa whaa whaa. The game did tell you. When you walked in that shrine and it said major test of strength and when you couldn't beat it. There. That's when it told you. Now you know. The game saves when you enter the shrine, so you lost out on maybe 5 minutes of your time.
And yes, open worlds do give excuses in being that. YOu can't have an open world game and hold a person hand at the same time.
I hope someday you get over your traumatizing experience of dying in Breath of the Wild.