My workaround for now, which I hope continues to work past Chrome 69, is to use Incognito-Filter to force all google.com accesses to open in Incognito Mode.

https://chrome.google.com/webstore/detail/incognito-filter/c...

This way I can log into Gmail and it won't log me into Chrome.

Obviously not ideal, and it doesn't excuse the deceptive and user-hostile malware Google just foisted on us, but it's a workaround.