That last episode gave the "Arthur is wilfully blind" argument some strength. Not that I think the show will go there, but it would make more sense. I kept hoping that if they don't have the magic reveal they'd at least let Arthur figure out who Merlin's father is, but no. And I really, really like that idea about Arthur sitting down and thinking for a bit.
Also, your theory about Sit Leon is totally canon! :(

Arthur not giving Merlin anything to defend himself with was weird. It's like he was thinking "we're all going to die anyway, so why bother", but then there'd be the question of why anyone else *was* wearing armour.