Maybe I'm misreading your intent here but this seems like a pretty silly statement. They are 25-23. That's not "play for next year" territory. I suppose you could mean don't trade long term assets for short term rentals given where they are but I'm not really sure they would be doing that anyways. I didn't like the concept of trading premium prospects for a closer last year but they only did it because they had no other solutions out there. In terms of this year, they are going to need pitching headed into 2018 anyways and odds are both Archer, Quintana, and maybe even Gray will be available. Cubs certainly will have trouble getting Quintana but the other two are realistic. Also supposedly pitt might listen on Gerrit Cole. Would be a tough sell in division but he's quite interesting.
Regardless, this team isn't that far off. They just need to find their bats. They've set their bullpen up to be very productive in the playoffs. Davis and Edwards have been basically unhittable. Uehara has been a strong performer as has Montgomery save for a few bad outings. Rondon and Strop haven't quite been what they were early last year but they are the 4th or 5th choice and they were the closer/set up last year. Cleveland rode that sort of bullpen to the WS last year and I'd argue while the cubs starters haven't quite been where you'd like, they are still better than what Cleveland used to get to the WS.
Long story short, my take is essentially they have the pieces they need they just aren't all running smoothly. That's going to happen in baseball. But let's not act like they are some sort of abomination here. The bats even with several young players underperforming is 9th in baseball in batting fWAR. The cubs starters are 10th. Oddly their relievers are 14th though I'm guessing that has more to do with Grimm and Dunesing as well as some of the other guys called up because the long games they have played. And this is arguably the cubs floor for 2017 barring injury and they are still roughly on a 85 win pace. The cubs don't need to win 100 games. They need to get to the playoffs which they are 4 back in the WC and 0.5 back in division to the brewers of all teams. Anyone really think they will hold? And sure if it's July and Schwarber, Contreras and Russell all still aren't hitting then maybe you worry a bit but their performance in the first 2 months only matters so far as getting to the playoffs and you'd rather them be hot heading into the playoffs then to dominate april and may and go cold in September. Obviously there's no guarantee they get hot but are we really going to bet against them for a full season when by in large their underlying numbers don't support that sort of sustained failure?
#1: Joe has kept Kyle in there. Add to it he has told him to ignore the numbers. He is playing the long term game with him. Not the short term.
#2: Even with the D being near the league lowest. They have not committed to Almora as the every day CF. They are even pushing Happ out there.
#3: Outside of Edwards and Wade the pen has been unpredictable.
#4: The O has been unstable.
#5: The pitching staff has gone back to the mean. Last year all 5 were having solid years.
Last year their D was the league best. The pitching put the ball into play into the league's best D. That is not the case this year.
The O was on more than off. We saw how last play offs how dependant they were on it. We are seeing it right now. They are wrecking the starters that are MOR quality and now they are going into some higher producing starters and the O gets shut down.+3
Now getting to your proposed trades. They feel very idealistic. In reality those teams are going to want a return package close to what the sox got from Sale. The Cubs only have 1 prospect that is top 25. Happ is a 2nd. But to gain A guy like Cole you are going to have to give up Eloy and either Happ or Baez. Add a top 3 arm in their system even to start talking to them.
Or they could just sit on the year and use their freed up resources to go after Yu Darvish. He will be 31 in Aug and would be a ideal option to go after. I can see the Cubs spending a equal deal to Lester. 6/155 mil. Then sit Darvish and Lester as the 1-2. Hendricks in as the 3. As a 4 you would want a lefty. I've liked Holland in F/A. I would prefer if they would push Montgomery into some starts this year. See if he would slot into the 4. He doesn't hit arb 1 until 2019 and to be honest the system just has no quality lefties. They have 3 quality righties.
So over all I really believe that any team gives up talent to save payroll when looking at trading for cheaper players vs signing a F/A. The Cubs are shedding 75 mil this offseason so this is not a issue at all. Except if they feel if they have 0% chance of landing Darvish then you have to think it over.
Hate to say this but if either Jake or John hit the DL and they let Montgomery start the team would be better off. Even if Montgomery didn't find success the loss is not huge and you have a better feel on the long term needs.