For private citizen purposes, such privacy is often effectively sufficient, but not complete.
To a snooping family member or evil maid, the browsing effectively didn't happen once the tab is closed.
People whose activities might lead to their being targeted by corporate espionage, copyright holders or state agencies would be kidding themselves to rely on browser privacy mode alone.
As technology evolves, nation states might move towards "full take" (China is well down this path now) and then progress to running AI against their rivers of data for "Full understanding" (China is progressing on this with their social credit system).
Governments of western countries try to follow, but due to pesky checks and balances must proceed more slowly and carefully, lest they lose their jobs. The Australian government's latest cyber security bill is another move to circumvent encryption and move back towards full take.
If they succeed, the move to "full understanding" will happen behind the closed doors of national security agencies, without meaningful oversight. We'll then be just a flip of a switch away from near-insur.ountable powers of totalitarianism.
Privacy in the digital age remains as important as it ever was. When companies like Google stand against the breaking of privacy, they are acting the best interest of private citizens everywhere.
It's also true that going dark, as complained about by government agencies, is a grave concern. Unfortunately, their approach is to advocate a cure that, while more convenient for them, is worse than the disease.