I like how both the angel and demon clans aren't wholly good or evil.
Both have their bastards, and both have their more reasonable members.
The real tyrants seem to be the supreme dieties, from what little we know of them. They don't actually participate in the wars, but what they did to Meliodas and Elizabeth makes them seem incredibly petty.
The fact they were fooled by a seven year old kid also doesn't make them look too smart.
Foreshadowed as an important character, yet you barely see him. He has the look and feel of a main character, and he's always treated as a hero at the start of a heroes journey with a ton of unlocked potential. Which creates an interest, that never pays off.
I think the reason he's there at all, is so the writer can have a faux main without all the wards and protections a main character brings with him. He can fail, he can be killed off, ect.
Which may have worked, if he was built at all as something impressive. But he wasn't.
He's not a Kamina, either. Kamina had all the makings of a main, which is why his death was so shocking.. Arthur only comes across as unrealized potential at best, and a "Womam in Fridges" plot device at worst.