Also, Lugh/Morgant wasn't trying to teach Ruairi to be good; he was trying to teach the numbskull to not blindly follow Morrighan and the Gods because they liked to play games, and that Humans were evil due to betrayal he experienced, further evident by Ruairi's dad being a jerk and offering his son to a dragon in exchange for power. He also goes nuts in G16, taking over the kingdom, believing Bella to being his daughter Triona, and then losing his mind when it turns out she isn't. If anyone's playing mind games on Lugh/Morgant it was Morrighan (who was responsible for Bella) and Cichol.
If anything, I'm still suspecting Piran to bepart of Vayne/Balor. Seriously, did you see Balor's mark? It's the Hymerark heart but with the left side flipped upward. Someone's trolling there. Anyway, weird as it is to admit, Balor hasn't really shown us any evil nature beyond leaving us in a room with an empty shell of his body that tried to kill us. Cethlenn deceived the Fomors while his boss buddy Vayne/Balor was running around with us and protecting two mortals from danger while we went after those black stones with the red eyes. Of course, that's just on screen. We don't know what he's been up to off of it.
Honestly, the fact that Vayne being who he really is was obscenely too obvious. He doesn't lack subtlety with that magma armor of his and that flashback. I'm really hoping it's just a case of 'he just doesn't care that much because what are you going to do about it?" or some sort of misdirection like "hey, i'm wearing the magma armor, but my real self is over there, lol".