One of the big reasons constantly heard for why the Nats need to bring back LaRoche is that he is a middle of the order lefty power bat. That is one of those baseball axioms that sounds true, but may not be so true when the numbers are examined closer. Point in fact for his career Michael Morse against right handed pitchers has hit .292/.343/.487 compared to the left handed LaRoche who has hit .274/.348/.495. Morse is slightly better at hitting for average while they both get on base at the same rate and LaRoche has slightly more power, but overall the numbers are very close.
The staggering thing with all this is the assumption is that left handed batters are so much better against right handed pitchers that a predominately lefty line-up is preferred to a predominately right handed one. But against left handed pitchers Adam LaRoche has hit .250/.305/.445 while Morse has hit .303/.357/.503. While there wasn't much difference between Morse and LaRoche against right handed batters there is a huge difference in them against left handed batters. The power is still their for LaRoche, but he is both hitting for average and getting on base at a rate below league average.
Expanding this out to the entire NL and the average right handed batter hit .249/.308/.392 off of right handed pitching while the average left hander hit .223/.285/.340 against left handed pitching. Perhaps the entire advantage of LaRoche in the line-up is that a manager may leave a lefty on the mound after facing Harper to face Zimmerman in order to get to LaRoche and Zimmerman for his career has hit .319/.399/.508 against lefties, but that is planning on a small confluence of events in order put more weight on LaRoche's impact on the line-up over Morse.
With Morse being as good as LaRoche against right handed pitchers and vastly superior against left handers defense is the final reason to choose LaRoche over Morse. UZR is not the best stat for ranking first basemen, but it is what we have and the numbers rank LaRoche as around a 5.0 UZR/150 in his last two complete seasons as a first baseman and Morse as roughly 0 or league average. Having watched both of them at first LaRoche is better at picking balls in the dirt and reaching for ball behind him, but first base is not the most defensively important position and the upgrade in offense provided by Morse evens out the downgrade in defense.
When everything is taken into account there may in fact be no overall difference in team wins with LaRoche or Morse at first base. Morse as an outfielder was hurting the team and removing his -20.4 UZR/150 from the outfield is the biggest upgrade the Nationals have made this off-season. To state it in simple terms if Morse were to provide 1.0 WAR of offense at first base the Nats have already made up for the lose of LaRoche without accounting for any offense that Denard Span provides.
The Nats face a sort of win/win situation here and that doesn't happen too often in baseball. If LaRoche walks they get two draft picks because of it, pay Morse $5 million to man the position, and then cede first to Tyler Moore, Matt Skole, or most likely Anthony Rendon in 2014. If LaRoche accepts the Nats two year offer then they trade Morse for prospects and hold Rendon in the minors for an extra year to be more prepared for the majors. The Nats truly are in a great position in these negotiations and while they would like LaRoche back, not only do they not need him, but they may be better off without him.