No guarantee doesn't mean that it isn't a probable position for one. Plus we're talking about Trading Tanev in addition to that for one guy. Dubois/Tkachuk may not even end up being as effective as Tanev is, and by all accounts Tanev is still young enough that he'll probably be an important piece of the next core.
There's no guarantee that you'll be able to find a defenseman that ends up as good as Tanev over the next three drafts even if you use every 1st rounder on D (which seems excessive and poor asset management to me as well). D are very difficult to draft and predict.
It just doesn't make any sense to me.
The player taken 4th overall has far more value than the player taken 33rd overall and has, at this point, a greater chance of becoming a high-end player in the NHL. I see no problem with moving up from 33rd to 4th, and if there is an overabundance of forwards, we can subsequently move that player for a defenseman of equivalent value from another team.
Columbus traded Ryan Johansen, the fourth overall pick in 2010, for Seth Jones, the fourth overall pick in 2013. They swapped one high-end player for another. That's a better strategy than picking 33rd and hoping that the defenseman drafted at that position becomes equivalent in value to the 4th overall selection. We significantly increase our odds of having a high-end player and can swap him for a player of equivalent value, whereas the 33rd pick is a far greater risk to become just an average player or even nothing at all.
Chris Tanev is not an elite defenseman, and I very much believe that to be a contender one needs to have elite defensemen; we will have the opportunity to pick the best players available. The loss of Chris Tanev will pay dividends for this team's future, improving our position in the next few drafts. The players we choose may be defensemen, or they may be forwards. At any rate, we will be able to move our 2016 4th overall selection if we are satisfied with the players we select in the subsequent drafts, or the best players available might be defensemen and we will be able to keep our high-end forward from 2016 while selecting high-end defensemen in the Top 15. Tanev will be 29 years old by the time Alex Edler is no longer a Canuck, and will be in his 30s by the time the time is highly competitive. He is a part of the current core group, but he will likely not be a member of a future contending group, or he will be less effective by that point.
Lots can change in three seasons. This team is in a rebuilding phase, and rebuilding requires present sacrifices and a plan for the future. Rarely do we have opportunities to acquire a top five talent in the draft.
If Dubois and Tkachuk turn into young, excellent wingers, we can trade one for a young, excellent defenseman. In that case, Tanev and the 33rd pick will have been used to make an upgrade on defense as well as to improve our draft position in the next few drafts. If Dubois becomes a great centerman, we'll have fulfilled our needs at center and wing, and we will also draft higher than if we were to simply keep Tanev and the 33rd pick.