Finally managed to find and fight Red Rider, and...kinda disappointed, since I beat him on my first try. To be fair, though, I got lucky with him never using or getting to use Antichthon. I read that you can get away with bringing at least two demons that null, repel, or drain fire, so I kept Uriel and Michael around for that, with Seth set for my fourth demon without any fire protection (I only brought him since mine had Doping, but I completely forgot my Michael had it too), then swapped out Seth for Demonee-ho on my second turn, who only resists fire. The only real problems I ran into were War Cry and Purple Smoke (along with a critical with one regular attack), but I had Flynn deal with the latter with Salvation and the former with a Dekunda Stone by the time I had my Uriel w/Dark Energy+Charge ready, using Demonee-ho to hit Red Rider's ice weakness with Breath (having had Michael use Archangel's Law on him for that on the third turn), with Flynn also hitting him with Antichthon a couple of times during the fight. By the fourth turn, I had my chance for Kannuki-Throw with a smirking Uriel, so I went for it and that was it.
That said, even if I didn't have something as overpowered as the same Uriel that I used to beat Masakado's Shadow on my team, I didn't consider it a particularly difficult fight based on how things were going for me. I wanted to beat the crap out of Red Rider after all of the trouble I went through to finally get him to show up, but I'd be lying if said Kannuki-Throw+Dark Energy+Charge+Smirk didn't take some of the fun out of it, as cathartic as it was to see.
You got really REALLY lucky I think.
I fought that guy over 30 times (for incense grinding) and he was using Antichthon every time (sometimes more than once per turn).
With that said, since you already did the DLCs, even with a bad pattern, I don't think he is a lot worse than Ancient of Days for example.
Anyway, congratulations!