Lafitte sending a message doesn't mean he's weak among the crew, especially since he stood unintimidated among shichibukai, and snuck into Majoria unseen. He must really be something.
I don’t see how delivering a nonthreatening message to marine HQ is an impressive show of strength. The marines are supposed to be the good guys remember, so why should he be intimidated, especially since he isn't a wanted criminal and doesn't have a bounty? With your logic Rockstar must be incredibly powerful and one of Shank's strongest, since he fearlessly stood in front of White Beard the strongest man and pirate in the world even though his bounty, the smallest of the group, says otherwise. Anyway I'm not saying Lafitte being Blackbeard's errand boy is evidence that he is the weakest of the group. I just feel that he is since traditionally the errand boy of a group is almost always one of the weakest of the group, and since he didn't appear with the others in that impressive chapter 233 double page spread. He didn’t even get a text box indicating his name and profession. Damn even Rockstar got a text box.
Now, my point was that fighters with the same profession tend to fight in One Piece. First of all, it give the characters a way to relate to each other. I doubt that Chopper would ignore a fighting doctor.
There's been only one instance of a Straw Hat officially of a non-fighting profession fighting another fighter of the same profession and that's when Sanji fought with Wanze, so cook vs. cook. That's certainly not enough to indicate a trend or a tendency, not like fighting styles. Anyway since when did a Straw Hat need to relate to an opponent's profession to want to fight him or her?
I’ll admit that I would really hate it if the Doc Q fight turns into some ridiculously simplistic morality tale of good doctor vs. bad doctor where after some truly profound speech we're supposed to learn that all good doctors shouldn't deliberately hurt people. Well fucking duh! Then we're supposed to accept that Chopper is a better doctor than the other guy because he can beat the other guy to within an inch of his life, because like that other doctor is evil, shut up.
As for fighting style, don't forget that Doc Q also has bombs and apple weapons. Now, swordsmanship and bomb fighting are possible, but not likely. It doesn't seem like those two things can mesh. Meanwhile, remember how Chopper took all those bombs in the Mr. 4 fight?
You assume that just because he feeds apples laced with explosives to random people on the street that he fights with them. First of all, how lame would that be? My feeling on that is it's probably just something he does for kicks as a way to test a person's fate - fate and destiny seem to be big thing with all the Blackbeard pirates - and likely doesn't represent his fighting style.
Finally, here's something interesting I discovered.
In the bottom right panel is a prototype of the BB pirates shown as silhouettes. Notice how the left most silhouette in the background has an object that's quite obviously in the shape of a sword holstered to its back. From this at least we know Oda had a swordsman planned for Zoro when he first came up with the BB pirates. The only BB pirate with an object holstered to his back who fits this silhouette is Doc Q. I think this provides more support for a Doc Q-Zoro matchup.