So, it turns out Chrome 69 is a lot more than just redesign of the tabs and removal of the www from the url.
I'm using the Mac version of Chrome (Version 69.0.3497.81 (Official Build) (64-bit) to be pedantic).
Up until two days ago, logging into gmail and logging into chrome were two different things, as they obviously are (one is a web service the other is a web browser, to be pedantic again)
I would usually be logged into gmail in the browser, but would only log into Chrome on special occasions and/or with specific accounts.
As of today, if I hit www.gmail.com and log in, I'm automatically logged into Chrome. If I log out of Chrome, I'm also logged out of gmail.
This can't be a bug... can it?
At least in the last version, clearing your private data (ctrl-shift-delete) no longer deleted Google cookies. To completely log out required manually digging into the advanced settings and then rebooting the browser.
Google fundamentally doesn't respect user privacy, and people should use Firefox.