Reb, I don't disagree that the Cubs are going to look to decrease K's. I disagree with you about how meaningful the change is going to be.
Let's say the Cubs bring in 2/3 of Span/Heyward/Zobrist. If I read your numbers correctly that would reduce the Cubs K's by 168. Let's give them a BABIP of .330 on those K's now balls in play. I'll round up and say that will add 56 hits. That would be an extra 0.35 hits/game. With a decrease in HR's it is certainly possible that the Cubs could score less runs. Unless you are going to get the Cubs into Royals/Giants territory of K%, it is just making improvements on the margins.
Another way to look at this is you could give the Cubs a hit/inning (single/double/triple) in every games and increase their hit totals by 1,458 and you wouldn't guareentee the Cubs one extra run without proper sequencing.
Not talking about substituting a generic low-K guy for an incumbent more productive high-K guy. Or, put another way, not advocating downgrading a position, overall--including defense-- intentionally.
The guys I mentioned are likely superior WAR players overall and help balance out a weakness in the club's profile. Fine with more Ks than average NL--with homers and walks. Love homers and walks but there is lack of balance on this club. Dwarfed 2nd worst K club. So, when a couple positions become vacant, a good idea to seek replacement guys who profile supporting a more balanced offense.
Point is you can do this without disturbing club's core. You can reduce by 200 Ks. That would make Cubs about 50 Ks more than NL average--which is no problem.
Diversification is good. More ways to score runs. Putting balls in play helps score runs, even without hits. Move baserunners. Score some runs on outs. Put more pressure on defense. Not advocating a small ball offense but rather an offense that can score without a walk and a homer. So, this is not entirely a matter of counting up hits. Lots of different ways to score runs, rather than being a one-trick pony.
Not advocating giving 700 PAs to Tommy La Stella but there are productive players out there who strike out less than 100 times and when you have positions striking out 165-189 times, why not fill those vacant spots with guys who do some things that your power guys don't do well.