The Manichees Are Going To Hell

So, this doesn't really reflect my theological views but I thought I'd connect some things here. So according to the Inferno, the sixth circle of Hell houses the heretics. From what research I have done, the Manichees seem to pick and choose from different religions and kind of piece stuff together to create their beliefs, even borrowing from Christianity. So wouldn't mixing Christianity with pagan religions be considered heresy? So, with all that said and basing this off of the texts, the Manichees are gonna burn.