Their security people are top-notch. They guard your data very diligently. If they did not, you would not trust them with intimate details about your life.
Your privacy is the same. They will keep your data private *from their competitors*, but they will fully enjoy using it for their own purposes.
It is ludicrous to think that an advertising company, whose value proposition is precisely in its ability to target users accurately, would willingly impair their ability to do so.
They will, however, gladly make it difficult for their competition.
At all.
It will ban 3rd party cookies the moment Google decides it's time to kill off most of their competition. They have Chrome installed on most people's computers and smartphones so they hold tremendous power to dictate the direction of the web, while they keep tracking people through the browser, with a user login, basically cookie-less.
"Once these approaches have addressed the needs of users, publishers, and advertisers, and we have developed the tools to mitigate workarounds, we plan to phase out support for third-party cookies in Chrome. Our intention is to do this within two years [from January 2020]." -- https://blog.chromium.org/2020/01/building-more-private-web-...
Want to bet on whether Chrome still supports third-party cookies, say, by the end of 2023?
(Disclosure: I work for Google, speaking only for myself)
How?
You do know that Google is a web advertising company first?
If they're proposing something, you can be damned sure that it was vetted first by people who know how to use it for ad tracking - because that's literally their bread and butter.
Chrome will never: ban 3rd party cookies, tell which sites track you etc. They're not going to shoot themselves in the foot without a plan.
There is no situation where Google will actually care about privacy, since their whole business model exists on the fact that they know everything about their users so they can target ads better.