I agree with your concerns.. Shogo is not a sure thing.
But honestly, I think a lot of his value will come from the glove.
If he's a flea with good (doesn't have to be great) OB and solid defense in CF, that's a very valuable complimentary starting player (and is being paid as such)
I agree with you, it's not likely that Shogo fixes the offense, but Senzel definitely wasn't the answer either.