This is the basic disagreement right? I don't necessarily think Zimmerman will be a liability in LF. I think he can be pretty average there, albeit with a weak arm. I absolutely think Werth will be well below average in LF, but with hard work might be able to be an average 1B. I think anybody should be able to be an "okay" 1B really.
I actually think Zimm could be a GREAT first baseman. Doesn't solve Werth's decline in the OF. ALR is considered very good, and that's all based on his skill at picking throws, certinaly not on his range on batted balls. Zimm, with practice, should be just as good at fielding throws, and would immediately have better range. I think with half a season under his belt, he'll be a more valuable defensive first baseman that ALR, even with being right-handed.
I think we squeeze 1 more year out of Werth in the OF (maybe LF, probably still in RF (ugh)), and then he moves to a super utility role (1B, LF, RF, DH in AL parks) for his last 2 years. My guess is next year's OF is the same, with Taylor and Souza taking over everyday jobs in 2016.
2B is still the hole to solve, bc I doubt we re-sign Cabrera, and Danny seems to have proven he's not the answer.