They are going to explain about the sword/amulet choices, so we'll see there.
About Brian and Roma. I think he didn't get any extra powers after his ascension to kinghood (hhehe). Why didn't Roma help against Morgan.... well, knowing Roma a little.. . who's to say that the whole Morgan thing wasn't a manipulative lie made to create ms Leigh? I mean, I found it very surprising to see Morgan in Otherworld just like that. My mind did not immediately race as to why didn't Roma help, but to why didn't Meggan help? Perhaps, Roma, Brian and Meggan concocted a plan, made Meggan disguise and Morgan, and so elaborate the circumstances to create a new 616 Cap Britain. It's would be too far-fetch, since Roma was responsible for tons of little manipulations to create Excalibur in the first place