AA has made it clear that his first priority this winter will be to improve the starting rotation. However, I think many people out there have a misconception about this need that I'd like to correct. Just because the offense has shown that it can be good as is, and the pitching needs serious help, does not mean that AA should put all of his money and resources into buying and trading for pitching, while ignoring opportunities to improve the offense unless something happens to fall in his lap.
The argument is simple, but I think in light of the way people have been talking, it needs to be stated. The bottom line is that the team needs to win more games. You can accomplish that in two ways: by either allowing less runs, or by scoring more runs. Winning a game 7-5 is just as good as winning it 4-2. The Rangers made the playoffs with a great offense and a disaster of a rotation, and the Rays competed with below average offense but top pitching. If you'll indulge me for a gross simplification of the advanced stats just to clarify my point, if you can add a player who will provide more WAR for your team than what you already have, that will help you the same whether they are a pitcher or a position player.
The name of the game, then, is just to get as many players as you can that will provide more WAR than what you already have at that position. The reason AA will look first to obtain pitching help first is because besides for Romero and Morrow, there aren't many guys here we can count on to provide much WAR. For example, say we're looking to get two pitchers to replace Alvarez and the other vacant spot in the rotation. Alvarez provided about 0.5 fWAR this past season, and options freely available to the Jays at this point would be basically replacement level, meaning about 0 WAR. If we could replace each of them with pitchers who will get about 3.0 WAR each, we'd be 6.0 WAR overall better off. On the other hand, many position players in the Jays lineup are better than replacement level already, meaning it's harder to find replacements for them that will provide a huge boost in WAR. Even when you consider the holes at 2B, LF, we can assume that Gose or Rajai Davis or Aviles at least have the potential to provide 1.0-2.0 WAR in a season, so to get the same 6.0 WAR improvement at 2B and LF would take getting players that each provide 5.0 WAR. This is pretty hard to do since players like that are hard to find, and expensive. But, for example, if the Jays were able to land Justin Upton and Ian Kinsler to fill those holes, that would be as worthy an expenditure than getting two good starting pitchers.
Pitching is the first place to look because we have so little of it. It's easy to accumulate extra WAR when replacing guys that gave you very little value. In other words, the reason pitching is a priority this winter is simply because of convenience. It's not because contending teams need to have balance between good hitting and good pitching. Rather, it's because pitching is just the easiest place for the Jays to build up extra WAR.
This should illustrate that the goal here is accumulating more WAR. The best way to do that is by replacing low WAR players with high WAR players. Right now, that seems easiest to do with pitchers, but doing so in the offensive positions where help is needed would also be just as good. Ideally, of course, it would be nice if AA could pull off both of these tricks.