After much scouring I found two more great fairy fountains, and after much farming guardian stalkers for cores and ancient gears I managed to upgrade my ancient armor to level 2, plus level 3 for the cuirass. It certainly helps the almost dying to one hit from everything problem, but not quite as much as I hoped. Guardians are much less of a problem now, but moblins are still surprisingly deadly.
None of that compares to lynels though. 21 hearts plus upgraded ancient armor, but 2-3 hits and I'm dead. Lynels are pretty optional for the most part, but the two I fought in Hyrule castle gave me a run for my money. I ended up losing all of my shields to the second one, but with Mipha's Grace I survived.
Anyway, the lack of shields and Mipha's Grace was a bit of a problem for fighting Ganon, but for fun I gave it a go without retreating to rearm. To my surprise, I won on the first attempt, but mostly through eating the hundreds of mushrooms, crabs, snails and roasted crow drumsticks in Link's pockets.
That said, the fight with Ganon kind of cemented in my mind that I'm not sure I like where the setting has started going. The game was absolutely fun and I put probably 60 or 70 hours into it, but... I mean, the game has had a few WTF moments, but Ganon was an OMGWTFLOLBBQ moment when he showed up. I felt like Link accidentally stepped into a Silent Hill game or something.
Which isn't to say that the Zelda games haven't had horror stuff in them before (thinking of you, Dead Hand), but between that, the plainly bizarre bosses, ancient robots all over the place and Link's magical smartphone / tablet, I wouldn't even recognize this as a Zelda game if gorons and zora weren't in it. It's a fun game and I really enjoyed it, but something feels off. Maybe my nostalgia for Ocarina of Time, Majora's Mask and Twilight Princess is too strong. I mean, I'd like to see a magic bar again some day, for example. And I know Skyward Sword had lots of the ancient robot stuff in it too for some reason, but something about Skyward Sword was off-putting from the very beginning to me. I never fully enjoyed playing it for reasons I've yet to understand, although I suspect it was just too frustrating.
Of course, having not played any of the handheld games, I've probably just missed things that have been working their way into the setting for a long time.