I don't think that Edge switching to Chromium means, that Edge will become "a slave" of Google.
Until now, Chromium has been strongly driven by one huge player: Google. Now, it can become driven by two huge players. It can erase the monopoly of Google over Chromium. Or if they have too many disputes, Microsoft can "fork" Chromium (like Google "forked" WebKit into Blink) and make their own, even better Chromium (Microsoft does have enough money and smart people to do so). The Edge could even beat Chrome, and be a new open-source multi-platform browser, which improves much faster than Chrome.
No. Even from git history, it's hard to actually quantify for Chromium, as most Google contributors use chromium.org emails, which obscures affiliation. The MS numbers are even less public.
Almost all the commit volume in Chromium is from Google engineers; even the largest external contributors (Opera and Samsung, last I knew) were a tiny percentage of commits. Individual volunteers practically don't exist: they're well under 1% of commits.
Until now, Chromium has been strongly driven by one huge player: Google. Now, it can become driven by two huge players. It can erase the monopoly of Google over Chromium. Or if they have too many disputes, Microsoft can "fork" Chromium (like Google "forked" WebKit into Blink) and make their own, even better Chromium (Microsoft does have enough money and smart people to do so). The Edge could even beat Chrome, and be a new open-source multi-platform browser, which improves much faster than Chrome.