Hey there,
something strange happened today when I decided to do the Brawler's Guild achievements before they take it out of the game.
I was just too bad to kill Yikkan Izu and died several times. So I queued for my next try when I suddenly got ported in an ongoing fight of someone else (don't know which boss he was fighting, tho). The NPCs he was fighting even were hostile for me. However, he died after a few seconds and we both got ported out. I then queued for another try, got ported in and suddenly had to fight against GG Engineering - the Boss after Yikkan Izu. So I figured that I effectively skipped one boss and was indeed rank 7.
Just wanted to share this with you as you maybe want to try to replicate this. Or does anyone maybe know what happened here? Anyways, I'm happy as I don't think I would have been able to kill Yikkan :P