Overall very well said.
I will mention LoZ and Zelda 2:AoL though. They were not stupidly hard compared to other games in their era. I know as Zelda 2 was the first NES game I played back in the day. Both games just took some practice to get good at. Both games were not even close to the toughest thing on the NES. Ghosts and Goblins? Battletoads? Super Mario Lost Levels? (just 3 examples of many) Yeah much harder. Not for good reasons too, too much trial and error there so you know exactly what to do in these three games. LoZ 1&2 on thge other hand, yeah not so hard with a little practice.
If you think Zelda 1 and Zelda 2 are very hard then you'll honestly struggle on many of the other NES games out there as they are much harder.
I honestly think there has not been a truly hard main series Zelda game. Sure we had TFH which can be tough playing solo and HW, where some of the adventure mode squares are juast unfair, but for main Zelda games, none of them are super hard. 100%ing Majoras Mask is hard due to some of the masks and heartpieces being hard to get, but that's it really. Zelda games get hard sure, but Dark Souls hard? Nah, none of them do.
1/1/8, 8/1/1, 1/8/1 runs of Zelda 2 do exist. Some people are crazy enough to attempt them. I am not. But I did do a dark deathmountain run. As in getting the candle before the hammer in Zelda 2. I often do that cause I like doing it. I even took a vodei of me doing it once a couple of years ago.
https://www.youtube.com/watch?v=pPDkeZ4MDBY That's it.
BotW looks like it could be a very hard game though. Not because it's solely being different to all LoZ games before it. I believe this is the kind of game that appeaks to the younger gamers (ie most of the development team that worked on it.) This is a great thing. A fresh perspecive on the series, not jsut the game old heads basing every Zelda game on Nostalgia.
You say "Adults (likely) want to feel like they just stopped Hell on Earth.". Some do like this in their games. Some don't. We're all adults though. Some just like good Zelda fun without being insanely challenged on every step of the way. This is why I like hero mode. So everyone is happy. You can choose to play it or not. I personally perfer not playing hero mode in Zelda game, but I know others who only play Hero mode on those Zelda games. Something for everyone. I do think the difficulty in BotW will not be hero mode, but in what order you do things. There will be a harder way and an easier way. The player will work out pretty quickly if a way is too hard and look for another easier way.
We needm to remember this is Nintendo. Many Nintendo and Zelda games do not like suepr difficult games. They just want fun. Aonuma and co needs to cater to them as well as the harder game fans as well. If BotW is Dark Souls in Hyrule, then I'll probably put it down as it's not what I look for in a Zelda game. But if on the other hand the game's difficulty is well balanced then I'll give it more of a shot.