You still want good defense, especially at 1B.
A quick spot check of the games in which this guy made poor plays . . . all were on base hits to RF. I looked at 5 or 6 of his poor plays, they were ground ball singles to RF, a bloop single to RF, and a double down the RF line.
That's all due to his poor range. His poor defense is giving up an additional 20-25 hits a season, which otherwise may have been outs. Those additional hits are sometimes turning into runs, and those additional runs may be turning into losses.
This guy needs to either be a DH (where he can do no defensive harm), or you can "hide" a guy like him in RF (see MikeT's "The Rightfielder" thread).