GIS vs CAD HELP!

Can anyone direct me to a source, or provide me with some non-technical explanation as to the benefit of using GIS over CAD to draw 17000 maps containing about 60000 parcels needing several layers of data. I'm not the GIS tech, but I am the union rep, and GIS dude's supervisor wants everything done in CAD, while the map guy says GIS is the best and most efficient way to create the maps. I've tried to educate myself and understand a little, but I need to be able to dummy it down for the elected official to support the map department's stand, if the GIS tech is indeed right about this. Can anybody help me?

Obviously a heated topic of discussion but really, if you want the most bang for your buck and you'd like to enable your departments to share their data and basemaps etc... then GIS is a no-brainer. Check into AutoCAD MAP / MAP3D and you'll likely satisfy both departments as they have a goal of bridging that gap