Well, I'm gonna say it now that it might as well be dropped and all parties move on from the issue.
I was about to say "Who knows what Aqua experience in the RoD" then I remembered we are actually going to see a bit of that soon xD Whoops!
In the end, I imagine every characters has something to teach to each other and any perceived hierarchy won't exist at all between these characters. Nobody will see anybody as better or stronger than the other. They will merely teach each other, fight alongside each other, and become friends and comrades.
The title of Master is useless, in that way, at least.