Wholly agree here with both of you. If there's anything that was scuffed about the first game, it was how easy the final boss fight was. Personally, although I felt like getting all the divine beast upgrades wasn't required for you to beat the game, I still felt compelled to complete those quests in order for me to get the full experience of the game's story and to explore the different areas or dungeons the game had to offer. People can make the argument with "well if it was so easy, why didn't you just not use the heart vessels or stamina upgrades? Just fight him without any upgrades and bam, you'll be challenged." The only issue I have with that argument is that I felt the game nudged players otherwise even if not explicitly stated: go and collect those upgrades, beat the beasts, get those Korok seeds, then defeat Ganon. Sure those decisions were made of my own volition but still when I think of my first playthrough, I never really knew just how easy it would've been with all those upgrades—and it would've been impossible to know that before I ever beat the game for the first time. I think no matter which side of the argument people are on though, both can agree that dark beast Ganon was a joke of a fight.
I think having much more incremental difficulty no matter where the player is on their journey would make the fight more worthwhile and fulfilling. Just take Sakurai's words for this concept from his "Squeeze and Release" video where he said that "stress on its own isn't fun, but if you really squeeze a player, then woosh! set them free, it can bring great satisfaction." I hope I haven't misinterpreted or misunderstood the point of his statement but that concept is probably why stressful games like souls games are so popular—the satisfaction received for defeating a very difficult boss is immense, and now you get to continue the journey. Not saying that TOTK will have souls-like difficulty with its bosses, but I do hope that it'd be more difficult than what we saw in BOTW.