Image Sharpness of Type...

We have a client that, against our suggestions, provides us with postcards that are 300 ppi raster files. They have small type on them that seems looks rather jagged of course. Here is what I don't understand. Part of the same raster file is printed on the press and then type is later imprinted on our Xerox 7760 because it is variable data. For some reason, even though it is the exact same 300ppi file it looks noticeably sharper on the press than it does on our 7760. The type is white and reversed out of a photo. It is around 5 point type.

Would another brand or model of laser printer work better for this?