...for many users...What numbers, precisely, do you have on this? Because it sounds to me as if you're arguing from a position of ignorance.
There might be some benefit to the small number of users who 1) have multiple devices and 2) share one or more of those amongst several other people in the same account in ways that this Chrome feature ... might address. But this doesn't strike me as some overwhelmingly large use case.
The system for user separation on shared computers is called ... user accounts. Which every mainstream consumer operating system has supported for the past 17 years (Windows XP being the latecomer to this game.)
Otherwise, this is a broadening of Google's ever-expanding ingestion of user data, either directly or by way of one more (or an incremental series of) "small change". If I notice my enemy maneuvering me to his advantage, I counter that maneuver. In my case, it's meant uninstalling Chrome and Chromium from any systems on which that's possible.
(My much-regretted purchase some years ago of an Android tablet being the primary exception, though I'm resolved to not repeat that mistake, despite a dire lack of viable market options presently. Purism and Ubuntu may be nearing useful products.)
...small changes...
In the Universe in which I inhabit, Google specifically addressed user feedback and sign-in changes. I cannot find your characterisation of their announcement as accurate under any charitable interpretation.