Yeah, that boss was easily the hardest I fought and agreed best boss arena. Just getting onto the arena took me a few minutes of "uh, where do I go lol? Oh. . .you just drop onto it." Sad thing is, he's an optional boss so unless you knew what to do, you'd skip it entirely playing through.
To counter your point on RNG, gaming the system is one thing to bait bosses into a pattern that's easy to beat but I'd rather just master the combat system and be able to count on a static set of moves to dodge and counterattack. Point being, I want to feel like I mastered a fight, not "I got lucky".