Switching off Chrome is like "voting with your wallet", because you're increasing the market share of another entity / project, increasing its legitimacy in the eyes of your friends and colleagues or in the stats that all major websites are collecting on browsers.

But switching to Chromium does none of that.

Also stripping Google's integration out of Chromium leaves you with a much less capable browser. Are you, for example, willing to use Chromium without Google's Chrome Web Store?

I don't think so. But say that you're willing to keep using Google's Chrome Web Store, Chromium is open source, but the Chrome Web Store is not and all those extensions, reviews and users can't be moved, so what will happen if Google decides to disallow access to its store to Chromium users?

If you think that can't happen, consider that they did it for AOSP Android and that alternatives to Google Play might as well not exist ;-)

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If you're worried about Google's control of Chrome, switching to Chromium does nothing useful, the project is still under Google's control, you're still depending on their good will and you're doing nothing to diminish Chrome's dominance of the market.