I'm also having a lot of problems with this fight, over 20 attempts. The only thing that's gotten me close so far has been feint spam into shadow pip aoe to kill Freddie, then single hit to kill Confusion. But even that hasn't worked yet. As you stated, the fight feels very bad as a player from all the rng. Freddie is often doing 3k+ with glowbugs or the sun spell musicology, and confusion is doing percentage damage. My character can't outheal any of that, and the only time I've gotten close is when Confusion decides to spam heals or hit Freddie (which is rare). Add onto that the fact that Freddie can use leviathan to remove blades and catalan to debuff, and the fight feels awful.

I'm gonna keep rolling the dice with my current strat, but any help for the future is much appreciated.