What rights do you give up by using an OS that is almost entirely open source? (keep in mind Linux has closed source parts too, some drivers for example)
If you dislike the paradigm that's fine, but don't claim it's hurting your freedom when
a) it's open source and
b) you can modify it the way you see fit.
Heck, you can change the Chromium OS source, recompile it and throw it on a Chromebook if you want...
Please, there's web caching, app manifests, and all sorts of other ways and standards to create web apps which run 100% on the user's machine. Applications need not be behind an SaaS wall anymore than video games need online DRM....
And Chrome OS absolutely IS an OS. The fact that it's centred conceptually around the Chromium browser and Google's proprietary bits doesn't make this less true.
If you dislike the paradigm that's fine, but don't claim it's hurting your freedom when
a) it's open source and
b) you can modify it the way you see fit.
Heck, you can change the Chromium OS source, recompile it and throw it on a Chromebook if you want...