Both fix it by making snooping and spoofing unavailable by default. An application only has access to its own windows, inasmuch processes are properly isolated

Both fix it by making snooping and spoofing unavailable by default. An application only has access to its own windows, inasmuch processes are properly isolated in other aspects as well. Typically they aren't, e.g. very few distros have any "single user level" safeguards for ~/.bashrc. Qubes solves that problem as well.