This lockdown mode looks like what ought to be default security behavior.
With a bit of luck, this will cause site operators to reduce their usage of unnecessary JS, so maybe this has positive impacts :)
My sense is that the functionality to provide those experiences resulted in a decrease in user security and privacy when they were introduced -- and that those risks were widely-discussed and well-understood.
It's weird (although not unexpected) to see the reversal of them touted as a selling point.