This isn't an attack on UI/UX people, it is only to suggest perhaps that industry would be better structured if everyone worked at agencies that recovered an employee's yearly salary in exchange for a month of their time. No pointless work generation that hurts the masses just to hit bonus targets.
If you're calling it "pointless work generation that hurts the masses", there must be something dysfunctional about your past experiences with UI/UX design people / processes in the organisations you've worked in.
(That's not to say that you shouldn't A/B test churn, but...)
For what it's worth, Google Analytics had this since forever ago (quite possibly since the acquisition of Urchin). It is one of the few standalone products at Google (rather than a feature of another product, like Hangouts) which shows a marketing splash page when you're already logged in.
At least now it says "Access Analytics" (new as of a few months ago) instead of two "Login" and "Signup" buttons which both did the same thing.
I haven't seen this new Gmail landing page yet, but I'm skeptical that it'll show up for users who are already logged in.
Nope like I mentioned it does this even when I am logged in, so no chance of cookie clearing. However I tried it again just to be sure, no luck. Two tabs opened, the second one a few seconds after logging into the first one, still lands me on marketing page.