BM needs to consider not only his top six defensemen, but also 7 - 9 depth. Given the injuries that any hockey team has during the season, let alone the Ducks of the past few years, depth on defense is absolutely necessary. If we assume that the top three defensemen are set for the Ducks, they need three additional defensemen plus spares. I think that the Ducks look to Larsson for one of these three positions, and possibly Guhle and/or Dotchin for the other two. Guhle may benefit from more time in the AHL and Dotchin may have some unknown issues, so neither is a sure thing. I could see BM signing a vet as well for stability and depth, although that has not worked out well in the past.
I like the potential physicality of Dotchin, but I am unsure if he is going to be able to last a full season. I am willing, however, to give him a chance if the team is otherwise satisfied with his personal situation. I have not seen enough of Guhle due to his injuries to really know enough about whether he can play at the NHL level at this point in time.
The Ducks stand to lose Holzer, Megna, and Welinski as UFA's, and I don't see anyone at San Diego other than Dotchin if you don't put him in the top 6 that would even fit as 7 - 9 depth at this point in time. I would probably see if I could sign two of Holzer, Megna and Welinski as 7 - 9 defensemen. Holzer seems to me to be a good #7, in that he can sit in the press box most of the time and still perform at a minimal NHL level when called upon. While I don't think that ay of the three are great, they can be serviceable for a time if needs be.