Sword Saint took me painfully long, too. So hard. He was one of those fights that a part of you asks, can I really do this? I could no-hit his maiden phase on later playthroughs (I got the Plat so ended up really digging in) but after that, I felt every bit a flawed shinobi, lol.
I have a personal theory on Elden (no idea how contentious or not this is) that it's not a SP game in conception but a coop one rather – From's first in fact, and this why the boss designs stray from more traditional Miyazakian fights. Examples are largest-ever HP bloat and unreasonable ATK chains meant for party combat. Anyway, small rant, but yeah, Radagon was tough but so many bosses in Elden were mega frustrating for solo tarnished. Malenia was stupidly hard for me in particular and an ugly fight even in subsequent playthroughs.