Certainly, allowing a deed based on the player's killing blows to advance based on some other player's killing blow is illogical.
But as for the concerns about Player B easily completing a deed and thereby acquiring a title in a manner that devalues a title already held by Player A:
You guys seriously pimp your titles and look at other people's titles? I turned off titles a long time ago. Heck, I often turn NAMES off. Too many words obstructing my view!
Reminds me, I'd better check to see if any of my toons still sports an active title. If so, it's probably from the Misty Mountains or something. How embarrassing!