Not really. It's been a year since my last playthrough but they killed me maybe once or twice a piece. Spectral Keeper was the one who killed me maybe five or six times.

Apart from her annoying status effects and the Mega-Death, Yunalesca wasn't very challenging at all.

Seymour Flux.... A lot of his fight is luck, to be honest. I saw a guy who fought Flux and got Cross Cleave which wiped out all his party except one but then Seymour did his Zombie/Auto-Life combo immediately after on his one surviving character.

That never happened to me.