Finally got time to read.
I have to say i didn't get their interactions as servant-master type. Where did you see a master who would let a servant to talk to him like that? It was (as you said) mostly that Arthur didn't want to talk about stuff and wasn't ready to open up. So he did everything to make Merlin stop talking.

And i'm very glad that they made Arthur somehow responsible for that slaughter. I expected it to be fully his father's fault but making Arthur responcible too made it more personal (for me as Arthur girl) and made the whole story more serious which is good cause i like what Bradley can do when given a good material.