But chromium and chrome do not lead to duplication of efforts:
Chrome is basicly Chromium + addons - and chrome devs contribute to chromium - they supplement eachother.
Chromium/Chrome are based on Webkit (forked into Blink since Chrome 27), which in turn is based on KHTML/KJS. Chrome was built in large part by former Mozilla engineers, and Mozilla Firefox itself was built based on the browser engine open-sourced by Netscape as its swan-song gift to the open web.
No. Google supports Chromium, and Chrome has proprietary additions.
I do wish Chrome didn't exist, but I'm not convinced that this comparison works.