>>41991837He's close to the top if not the hardest, depending on how you play.
If you're a completionist, then provided you're using zero shadow mons his pokemon's moves are ALWAYS supereffective on you regardless of type, he has three legendaries albeit weaker ones, and you're actively trying to snag as many pokemon from him as possible (made worse by the low catch rate of his legends). Even if you "beat" him, you'll most likely have to rebattle him a handful of times to snag the rest of his team.
If you're not a completionist and just want to play through the story, he's difficult but far from the most difficult. I had a harder time with evice.
