A DAE Collada file contains the geometry data.
When appropriate, there is also a folder of the texture images.
A KMZ is a re-suffixed ZIP file.
this contains a doc.KML file [used to interpret the other data for GE's purposes], and a subfolder named 'models' containing a very similar DAE file, and an images-subfolder [although the image file-names differ from a vanilla DAE] etc.
So if you extracted the compressed KMZ's contents it'd actually be slightly larger than a plain DAE and its images.
If the client now wants DAE files, then when they are uncompressed that's what they'll get - bigger files.
For 'transmission purposes' you could ZIP the DAE and its images-folder - then it'd be about the same size as the equivalent KMZ...
Of course they would need to extract the files to use them in their alternative 'Cesium' app and convert them into its 'glTF' format data - with GE the KMZ's contents are extracted 'behind the scenes', but it still happens !
I also see that there is a KML to CZML converter https://groups.google.com/forum/#!topic/cesium-dev/kHtl6MXvEFY
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