All Dell wanted you to do was uninstall the last update you installed to the version of Ubuntu that came pre-installed, not completely reinstall Ubuntu.
I don't believe Dell modified Ubuntu at all. My Dell tech contact said the WiFi+BT drivers were built into Ubuntu, and did not come from Dell.
Maybe you should start a thread on the Ubuntu forums (https://ubuntuforums.org/) where the experts can help you figure this out.
Forum Member since 2004
I am not a Dell employee